Iatrogenic and medication-induced hypothyroidism is a condition in which reduced production and biological availability of thyroid hormones result from medical interventions, diagnostic or therapeutic procedures, or exposure to medications and exogenous substances capable of interfering with thyroid physiology. From a practical clinical perspective, this chapter includes both post-procedural forms, such as those occurring after thyroidectomy, radioiodine ablation, or cervical irradiation, and forms induced or precipitated by medications that affect hormone synthesis and release, peripheral metabolism, transport and protein binding, iodine uptake and organification, or thyroid immunity. A further scenario, which is often underestimated, is “functional” hypothyroidism in patients already receiving levothyroxine replacement therapy, in whom concomitant medications or treatment-induced clinical conditions, such as malabsorption, changes in gastric pH, or intraluminal chelation, reduce absorption or alter requirements, producing a biochemical and clinical condition comparable to untreated hypothyroidism.
The clinical relevance of iatrogenic hypothyroidism lies in the fact that it is, by definition, largely preventable or detectable at an early stage through appropriate monitoring, although it may rapidly become clinically significant in vulnerable populations such as older adults, patients with cardiovascular disease, pregnant women, and patients with cancer receiving targeted therapies or immunotherapies. Severity ranges from subclinical to overt forms and, in specific settings, such as after ablative procedures or inappropriate interruption of replacement therapy, it may progress to major complications.
The epidemiology of iatrogenic and medication-induced hypothyroidism cannot be described in the same way as that of a single disease, because it depends on the prevalence and intensity of use of specific procedures and pharmacological classes within the population. In broad conceptual terms, there are settings in which hypothyroidism is an expected and planned outcome, such as after total thyroidectomy or radioiodine ablation for benign or malignant disease, and settings in which it is an undesirable but relatively frequent effect, such as during treatment with amiodarone, lithium, interferons, certain targeted cancer therapies, and immune checkpoint inhibitors. These are accompanied by “indirect” scenarios in which exposure to medications does not damage the thyroid but reduces levothyroxine efficacy or increases its required dose, resulting in increased thyroid-stimulating hormone levels and recurrence of symptoms in previously compensated patients.
A major epidemiological determinant is procedural medicine. The likelihood of developing hypothyroidism after surgery depends on the amount of residual thyroid tissue and the indication for the procedure. Total thyroidectomy almost inevitably creates the need for levothyroxine replacement, whereas partial resections may be followed by hypothyroidism depending on residual functional reserve, the presence of pre-existing autoimmune thyroiditis, and the ability of the remaining tissue to increase hormone synthesis. A similar mechanism applies to radioiodine treatment and external radiotherapy to the neck or upper mediastinum, which may progressively impair thyroid function, sometimes after a considerable delay, making prolonged follow-up necessary.
From a pharmacological perspective, the frequency of hypothyroidism is strongly influenced by the patient’s clinical profile and baseline thyroid status. The main shared risk factors include female sex, older age, the presence of thyroid autoimmunity, indicated by anti-thyroid peroxidase and/or anti-thyroglobulin antibodies, multinodular goitre or nodular thyroid disease, iodine deficiency or excess within the geographical setting, and a family history of thyroid disorders. Although these factors are not definitive causes, they increase the likelihood that a medication will act as a trigger or accelerator of progression toward clinical hypothyroidism.
Amiodarone is a paradigmatic example because it combines a high iodine load with direct effects on the thyroid and on peripheral thyroid hormone metabolism. The likelihood of developing hypothyroidism during amiodarone therapy is higher in iodine-sufficient areas and in individuals with latent autoimmune thyroiditis, in whom impaired escape from iodine-induced blockade or an autoimmune predisposition facilitates progression to persistent hypothyroidism. With lithium, risk increases with duration of exposure, age, and autoimmune predisposition. Psychiatric comorbidity may also make early recognition of symptoms more difficult, because fatigue, psychomotor slowing, and weight changes may be attributed to the underlying disorder or to other concomitant psychotropic medications.
In oncology, epidemiology is evolving rapidly because the use of therapies capable of interfering with thyroid function has increased substantially. Tyrosine kinase inhibitors and other molecularly targeted agents may induce thyroid dysfunction through multiple mechanisms, including vascular injury and regression of thyroid tissue, impaired iodine organification, and alterations in peripheral metabolism. Immune checkpoint inhibitors may cause destructive thyroiditis that frequently progresses to hypothyroidism, sometimes after an initial thyrotoxic phase. The epidemiological impact of this phenomenon is significant because symptoms may be attributed to the malignancy or to cancer treatment as a whole, creating a risk of underdiagnosis in the absence of a structured monitoring plan.
A clinically decisive issue is hypothyroidism caused by interactions in patients receiving levothyroxine. Risk increases in the presence of medications that reduce intestinal absorption or alter bioavailability, in patients with gastrointestinal comorbidities, or during enteral nutrition. In these cases, hypothyroidism is iatrogenic not because the medication damages the thyroid, but because the therapeutic pathway interferes with replacement treatment, producing a relative hormone deficiency that may become clinically significant if it is not detected.
From an aetiological perspective, iatrogenic and medication-induced hypothyroidism can be grouped into three major categories: loss or inactivation of functioning thyroid tissue, direct inhibition of hormone synthesis or release, and alterations in hormone metabolism, transport, or availability that reduce the final biological effect. These categories are not mutually exclusive and, in some settings, several mechanisms coexist, producing a composite and clinically insidious pathophysiology.
Loss of thyroid tissue represents the most straightforward mechanism. After total thyroidectomy, endogenous T4 and T3 production ceases, and homeostasis depends entirely on levothyroxine replacement. After partial surgery or incomplete ablative treatment, residual function may initially be sufficient and subsequently decline over time, particularly when autoimmune thyroiditis coexists or when the remaining tissue is ischaemic or fibrotic. Radiotherapy to the neck may cause progressive thyrocyte injury and microvascular damage, with an often slow course and a prolonged interval between exposure and overt hypothyroidism.
A second group involves inhibition of hormone synthesis and release. Under physiological conditions, the thyroid takes up iodide through the sodium-iodide symporter, organifies it through thyroid peroxidase, and incorporates it into thyroglobulin to form monoiodotyrosine and diiodotyrosine, which couple to generate T4 and T3. Medications and substances may interfere at several levels. Acute iodine excess may induce blockade of organification and synthesis, known as the Wolff-Chaikoff effect, and if escape is incomplete or ineffective, persistent hypothyroidism may develop. This mechanism is central to dysfunction associated with iodinated contrast media in predisposed individuals and, above all, during amiodarone therapy, which delivers large quantities of iodine and adds direct effects on thyrocytes and peripheral hormone metabolism.
Lithium reduces thyroid hormone secretion by interfering with thyroglobulin proteolysis and T4 and T3 release, and it may promote or unmask thyroid autoimmunity. In this setting, pathophysiology is dual. On one hand, there is a direct pharmacological effect on hormone release, while on the other, an autoimmune process may develop or worsen, making hypothyroidism more persistent and less reversible with modification of the medication alone. The interaction between predisposition and exposure explains why patients receiving similar doses for similar durations may experience markedly different endocrine outcomes.
A third pathophysiological axis involves alterations in peripheral metabolism and central regulation. Some medications increase thyroid hormone clearance or modify deiodinase activity, altering conversion of T4 to T3 and affecting thyroid-stimulating hormone levels. In oncology, tyrosine kinase inhibitors may induce a characteristic sequence of initial fluctuations followed by progression to overt hypothyroidism, sometimes associated with reduced thyroid volume and atrophy. In these forms, the problem is not merely reduced production, but also tissue remodelling and alteration of the response dynamics of the hypothalamic-pituitary-thyroid axis.
There is also a distinctive and clinically important mechanism in which hypothyroidism is central and induced by pharmacological treatment. The prototype is bexarotene, which may suppress thyroid-stimulating hormone and increase peripheral thyroid hormone metabolism, producing a condition in which thyroid-stimulating hormone is not a reliable indicator and management must be based on free T4 and the clinical picture. This scenario illustrates how a medication may shift the control point of thyroid homeostasis away from the conventional thyroid-stimulating hormone and T4 axis toward an altered equilibrium, with substantial diagnostic and therapeutic implications.
Immunotherapy with immune checkpoint inhibitors may induce immune-mediated thyroiditis, often destructive in nature, in which an initial phase of release of preformed hormones may be followed by depletion of thyroid reserve and subsequent hypothyroidism. In this pathophysiological process, the thyroid is not inhibited but progressively depleted by inflammation. Progression to hypothyroidism may be rapid, and the clinical picture may overlap with systemic effects of immunotherapy, making scheduled laboratory monitoring essential for timely diagnosis.
Finally, iatrogenic hypothyroidism may result from failure of replacement therapy because of reduced levothyroxine bioavailability. In this setting, pathophysiology consists of reduced intestinal absorption or increased clearance, with increased thyroid-stimulating hormone and reduced free T4. Mechanisms include changes in gastric pH, intraluminal binding by cations or resins, food-related interference, and iatrogenic conditions such as continuous enteral nutrition. At tissue level, the final result is the same: reduced thyroid hormone availability and consequent slowing of metabolic and adaptive processes regulated by nuclear T3 signalling.
The clinical manifestations of iatrogenic and medication-induced hypothyroidism depend on the speed of onset, severity of hormone deficiency, patient age, and comorbidities, with an additional variable represented by the clinical setting in which the disorder develops. In post-procedural forms, progression to hypothyroidism may be relatively predictable and, when replacement is correctly initiated, symptoms may be minimal. Conversely, in pharmacological forms developing subacutely, particularly in patients with cancer or cardiovascular disease, symptoms may be confused with treatment-related adverse effects, disease progression, or inflammatory syndromes, delaying recognition.
During history taking, patients frequently report fatigue, reduced physical performance, daytime sleepiness, cold intolerance, cognitive slowing, and weight gain or difficulty losing weight. In pharmacological settings, a temporal relationship may emerge with initiation or dose escalation of a medication, treatment cycles, or repeated radiological procedures. In patients receiving amiodarone or lithium, progression may be slower, and symptoms may be attributed to cardiovascular disease or neuropsychiatric effects, respectively, making precise chronological reconstruction essential.
Physical examination may reveal bradycardia, dry skin, dependent or mild myxoedematous oedema, delayed deep tendon reflexes, and hoarseness. However, many pharmacological forms are initially paucisymptomatic, and clinical manifestations become apparent only when the deficiency becomes more pronounced or metabolic demand increases. In patients with cancer, coexisting cachexia, anaemia, pain, and sleep disturbances may mask the contribution of hypothyroidism, which may sometimes present as an unexplained deterioration in treatment tolerance or as a disproportionate increase in fatigue.
A distinctive clinical feature of iatrogenic forms is the possible coexistence of manifestations related to the causal treatment. After surgery or radiotherapy to the neck, dysphonia, dysphagia, or symptoms related to alterations of cervical structures may coexist. These are not manifestations of hypothyroidism but contribute to the overall perception of illness. In immunotherapy-related forms, there may be an initial thyrotoxic phase with palpitations and tremor followed by hypothyroidism, and a history of this biphasic course is a useful diagnostic clue.
In patients already receiving levothyroxine, the clinical presentation of interaction-related iatrogenic hypothyroidism may be even more subtle. The patient may report recurrence of fatigue, weight gain, cold intolerance, or worsening constipation after introduction of a new medication or supplement, or after changes in dietary habits or timing of administration. In these cases, physical examination may provide little information, and recognition depends on careful history taking and targeted assessment of thyroid parameters.
Severe untreated forms may progress to cardiovascular complications, clinically significant dyslipidaemia, serous effusions, and deterioration in cognitive function, particularly in vulnerable patients. Although myxoedema coma is rare, clinical risk increases when hypothyroidism occurs in the setting of systemic illness, infection, or exposure to sedative agents, which is particularly relevant in hospital and oncology settings.
Suspicion of iatrogenic and medication-induced hypothyroidism should be systematic and guided by clinical context. It should be considered when symptoms compatible with hypothyroidism appear after a procedure involving the thyroid or neck, when a patient receiving medications known to interfere with thyroid function develops disproportionate fatigue, cold intolerance, or bradycardia, or when a patient already receiving replacement therapy loses biochemical control without an evident explanation. In many circumstances, iatrogenic hypothyroidism does not present as a completely new disorder but as a change in the individual set point following a therapeutic event. Comparison with previous values is therefore often more informative than interpretation of a single isolated result.
After total thyroidectomy or radioiodine ablation, suspicion is an integral part of the care pathway and translates into scheduled monitoring and levothyroxine titration. After partial surgery or radiotherapy to the neck, surveillance must be maintained over time even when initial results are normal, because injury may be progressive. In patients with cardiovascular disease receiving amiodarone, worsening bradycardia, reduced exercise tolerance, or an increased requirement for cardiovascular medications may be a clue. However, clinical manifestations may be attenuated or attributed to the underlying cardiovascular disorder, making laboratory support essential.
In patients receiving lithium, suspicion should increase when psychomotor slowing, weight gain, constipation, and reduced vitality develop, particularly when signs of thyroid autoimmunity coexist or there is a family history of thyroid dysfunction. In hepatological and immunological settings, interferon treatment or other forms of immune modulation should raise awareness of possible thyroiditis, which may initially present with fluctuations and subsequently stabilise as persistent hypothyroidism.
In oncology, suspicion is particularly important because many modern therapies have a clinically significant endocrine profile. In patients treated with immune checkpoint inhibitors, the development of fatigue, mood changes, bradycardia, or weight gain, particularly when preceded by adrenergic symptoms compatible with thyrotoxicosis, should prompt rapid thyroid assessment. In patients receiving tyrosine kinase inhibitors or other targeted therapies, surveillance should continue throughout treatment because the course may fluctuate before progressing to overt deficiency.
Finally, suspicion should be high when a patient receiving levothyroxine develops an increase in thyroid-stimulating hormone after introduction of medications known to interfere with absorption or metabolism. In these cases, the objective is not only to diagnose hypothyroidism but also to identify a modifiable iatrogenic cause, because correction may depend on administration timing, pharmaceutical formulation, or management of the interaction, in addition to dose adjustment.
The diagnosis of iatrogenic and medication-induced hypothyroidism is based on integration of clinical findings, thyroid biochemistry, and causal reconstruction. The first step is measurement of thyroid-stimulating hormone and free T4, interpreted according to the clinical setting. In primary forms, thyroid-stimulating hormone typically increases and free T4 decreases, whereas in subclinical forms free T4 may remain within the reference range despite elevated thyroid-stimulating hormone. However, diagnosis cannot be reduced to a fixed pattern, because certain medications and iatrogenic conditions create situations in which thyroid-stimulating hormone is unreliable or does not accurately reflect axis function.
After total thyroidectomy or radioiodine ablation, the diagnosis is often anticipated, and the main objective is to monitor the adequacy of replacement. In these patients, assessment includes thyroid-stimulating hormone and free T4 after initiation or modification of therapy, allowing sufficient time for the new steady state to be reached. After partial resection or radiotherapy to the neck, diagnosis is based on periodic testing because hypothyroidism may develop after a delay. In these settings, assessment of thyroid autoimmunity is also useful because it increases the likelihood of progressive functional decline.
In pharmacological forms, a key step is distinguishing true hypothyroidism from transient test abnormalities. Amiodarone, for example, may alter thyroid parameters even in the absence of clinical hypothyroidism, and diagnosis requires careful evaluation of trends over time, clinical findings, and thyroid-stimulating hormone and free T4 concentrations. Similarly, after exposure to iodinated contrast media, thyroid dysfunction may be transient or persistent in predisposed individuals, and diagnosis must be correlated with the timing of exposure and individual susceptibility.
In oncology, diagnosis is often guided by monitoring protocols. In thyroid dysfunction caused by immune checkpoint inhibitors, the sequence may include a thyrotoxic phase followed by hypothyroidism. Serial assessment of thyroid-stimulating hormone and free T4 is therefore more informative than a single measurement. In this situation, clinical examination and the possible presence of thyroid antibodies may help define the phenotype, although management is primarily guided by clinical and biochemical findings. In patients receiving tyrosine kinase inhibitors, diagnosis may be complicated by fluctuations and systemic comorbidities. The approach should therefore include evaluation of trends, symptoms, and functional impact.
A critical area is the diagnosis of pharmacologically induced central hypothyroidism, in which thyroid-stimulating hormone may be low or inappropriately normal. In these cases, diagnosis depends on reduced free T4 and the clinical picture, and it is essential to avoid the error of considering a normal thyroid-stimulating hormone level as excluding hypothyroidism. This scenario is particularly relevant with agents such as bexarotene and, more generally, in complex patients in whom medications and systemic illness may alter the hypothalamic-pituitary-thyroid axis.
In patients receiving levothyroxine, diagnosis of interaction-related iatrogenic hypothyroidism requires a meticulous medication history, including supplements, and assessment of administration timing in relation to meals and other medications. Increased thyroid-stimulating hormone and reduced free T4, in the absence of reported changes in adherence, require consideration of interference with absorption or bioavailability. In many cases, targeted modification of administration practices followed by repeat laboratory testing after an appropriate interval confirms the causal relationship and allows optimisation of therapy without excessive dose escalation.
A clinically useful classification of iatrogenic and medication-induced hypothyroidism begins with the distinction between post-procedural and pharmacologically induced forms. The former include hypothyroidism after total thyroidectomy, radioiodine ablation, and external radiotherapy to the neck, with a continuum ranging from immediate loss of function to progressive decline. The latter include hypothyroidism caused by agents acting directly on the thyroid, therapies that modulate immunity or induce thyroiditis, and agents that alter hormone metabolism and bioavailability.
A second classification axis distinguishes primary from central forms. In primary forms, the defect lies within the thyroid and the expected response is an increase in thyroid-stimulating hormone. In central forms, the defect lies in pituitary or hypothalamic regulation or is pharmacologically mediated, and thyroid-stimulating hormone does not increase appropriately. This distinction is not merely academic, because it determines test interpretation, monitoring strategy, and therapeutic targets. In central forms, management is guided by free T4 and the clinical picture rather than by thyroid-stimulating hormone.
From a temporal perspective, it is useful to distinguish acute or subacute from chronic forms. Post-thyroidectomy hypothyroidism develops rapidly when replacement is inadequate or discontinued, whereas post-radiotherapy hypothyroidism tends to emerge slowly. Immunotherapy-related forms may develop over weeks or months, often with a biphasic course, whereas lithium-related or amiodarone-related forms may become established more gradually and persistently.
Severity may be described as subclinical or overt hypothyroidism according to the biochemical and clinical profile. In iatrogenic forms, however, severity must also be interpreted according to context. Mild hypothyroidism may be clinically relevant during pregnancy or in cardiovascular disease, whereas in other settings it may be monitored. In patients with cancer, hypothyroidism may also impair treatment tolerance and quality of life, often making a more proactive approach appropriate.
A practical classification, particularly useful in outpatient care, further distinguishes irreversible from potentially reversible iatrogenic hypothyroidism. After total thyroidectomy or complete ablation, hypothyroidism is permanently irreversible and requires lifelong replacement. In some pharmacological forms, thyroid function may recover after discontinuation or modification of the causal agent, whereas in others, such as after destructive thyroiditis or certain cancer therapies, persistent deficiency may develop. This distinction guides counselling, reassessment frequency, and the strategy for a possible supervised withdrawal trial in selected and clinically safe settings.
Treatment of iatrogenic and medication-induced hypothyroidism is based on levothyroxine as the therapy of choice, with individualisation of dose and target according to age, comorbidities, pregnancy, the presence of cardiovascular disease, and the underlying cause. Management, however, cannot be limited to prescribing replacement therapy. In iatrogenic forms, it is often possible to act on the causal determinant, prevent further interference, and establish follow-up capable of reducing the risks of undertreatment and overtreatment.
In post-procedural forms, replacement therapy is generally stable and initiated early. After total thyroidectomy, the objective is to restore euthyroidism with an appropriate levothyroxine dose, followed by laboratory reassessment after a sufficient interval. In patients treated surgically for thyroid carcinoma, the dose and thyroid-stimulating hormone target may be adjusted according to oncological risk, although the fundamental principle remains the provision of adequate T4 replacement. After radiotherapy to the neck, replacement is initiated when hypothyroidism develops, but follow-up must account for possible progression of tissue injury and the need for dose adjustments over time.
In amiodarone-related forms, management requires balancing cardiovascular risk against thyroid control. Amiodarone-induced hypothyroidism can often be treated with levothyroxine without necessarily discontinuing the antiarrhythmic agent, particularly when amiodarone is essential for cardiac stability. Dose titration should be cautious in patients with cardiovascular disease, with gradual increases and clinical monitoring, because the objective is to improve metabolic function without producing hormone excess that could promote arrhythmia or ischaemia. Baseline thyroid status and the presence of autoimmunity should also be defined because they influence the likelihood of persistent deficiency.
With lithium, therapeutic decisions depend on the severity of hypothyroidism and the psychiatric need for treatment. In many cases, levothyroxine allows lithium to be continued when it is clinically indispensable, correcting the hormone deficiency and reducing its effects on weight, energy, and cognitive function. This approach is particularly relevant when hypothyroidism is accompanied by goitre or autoimmunity, settings in which lithium discontinuation alone does not ensure complete or rapid recovery.
In thyroid dysfunction caused by immunotherapy, treatment follows the principle of managing the endocrine adverse event as a condition that is often stable and treatable without necessarily interrupting cancer therapy. When hypothyroidism develops after immune-mediated thyroiditis, levothyroxine is introduced according to clinical and biochemical findings, with close monitoring during the initial phases because requirements may change during the transition. In oncology, continuity of anticancer therapy and reduction of avoidable hospitalisations often depend on rapid recognition and correction of hypothyroidism.
In forms caused by targeted cancer therapies, such as tyrosine kinase inhibitors, levothyroxine replacement is frequently required and may need more dynamic adjustment. Treatment must be integrated with the oncology pathway. Periodic thyroid testing is essential, and symptoms must be interpreted comprehensively because cancer-related fatigue and hypothyroidism may reinforce each other. In specific pharmacological conditions that induce central hypothyroidism, management must be based on free T4 and the clinical picture and may require higher doses or unconventional adjustments, with specialist monitoring and caution.
When hypothyroidism is caused by treatment-related interactions in patients already receiving replacement therapy, effective management often consists of correcting the interference. This includes optimising levothyroxine administration timing, separating it from medications that chelate or bind the molecule, considering alternative formulations in selected settings, and reassessing the need for certain supplements. A sustained dose increase is appropriate only after these determinants have been addressed, because otherwise a bioavailability problem may be managed with escalating doses that become excessive once the interference is removed.
The main objective of follow-up in iatrogenic and medication-induced hypothyroidism is to maintain a stable balance between replacement efficacy and safety, minimising residual hypothyroidism while preventing iatrogenic hyperthyroidism caused by excessive dosing. Because many causes are associated with ongoing treatment or permanent procedural outcomes, follow-up must be structured and adapted to individual risk.
After thyroid procedures, laboratory reassessment with thyroid-stimulating hormone and free T4 allows therapy to be titrated until adequate control is achieved, followed by stabilisation with periodic monitoring. In older patients or those with cardiovascular disease, titration should be slower and guided by clinical findings. In patients with oncological indications, follow-up must be integrated with risk stratification and the specific objectives of the oncology pathway, avoiding excessive fluctuations that may affect wellbeing and cardiovascular function.
In pharmacological forms, the follow-up strategy depends on the therapeutic class and the likelihood of progression. During amiodarone or lithium treatment, periodic monitoring is useful even in the absence of symptoms because onset may be gradual and clinical manifestations nonspecific. With immune checkpoint inhibitors, closer monitoring is required during the initial treatment phase because immune-mediated thyroiditis may develop early and change phase rapidly. During targeted cancer therapy, the frequency of testing should reflect treatment cycles and the individual patient’s previous laboratory course because thyroid function may fluctuate.
A key component of follow-up is periodic review of concomitant therapies and levothyroxine administration practices. In patients who lose biochemical control, follow-up should include a practical assessment of timing, meals, supplements, and newly introduced medications. In many cases, optimisation of treatment behaviour and removal of interference correct the problem without the need for substantial dose escalation.
When hypothyroidism is potentially reversible, follow-up may include reassessment of thyroid function after modification of the causal agent or completion of the treatment that induced it, always using a cautious approach. In some situations, particularly after destructive thyroiditis, deficiency may persist. In others, partial or complete recovery may occur. Decisions to reduce or discontinue levothyroxine must be based on structured reassessment with serial testing and careful attention to clinical findings, avoiding abrupt changes that could destabilise vulnerable patients.
Finally, follow-up must consider long-term outcomes, particularly cardiovascular and metabolic risk in patients with chronic hypothyroidism or repeated fluctuations in thyroid parameters. Maintaining stable control, especially in high-risk populations, is one of the most important objectives for reducing complications and improving quality of life.
The prognosis of iatrogenic and medication-induced hypothyroidism is generally favourable when diagnosis is timely and levothyroxine replacement is correctly initiated and monitored. In permanent post-procedural forms, outcome depends on the quality of follow-up and stability of biochemical control. In most cases, well-managed treatment permits a substantially normal life. In pharmacological forms, prognosis depends on the course of the underlying cause, the possibility of modifying the iatrogenic determinant, the initial severity of the deficiency, and associated comorbidities.
The most important complications are related to two extremes: unrecognised or undertreated hypothyroidism and iatrogenic hyperthyroidism caused by overtreatment. Undertreatment may contribute to dyslipidaemia, worsening cardiovascular function, reduced physical and cognitive performance, and, in vulnerable patients, increased risk of hospitalisation. In oncology, uncorrected hypothyroidism may increase fatigue and reduce treatment tolerance, affecting continuity of care. In severe forms, particularly in older adults or patients with intercurrent disease, the risk of systemic complications increases and severe metabolic decompensation may occur.
Overtreatment, often resulting from dose increases that are not recalibrated after removal of a pharmacological interaction or after changes in body weight and comorbidities, may cause tachycardia, arrhythmias, bone loss, and neuropsychiatric symptoms. In ischaemic heart disease or atrial fibrillation, even moderate excess may be clinically relevant. Prevention requires cautious titration and structured reassessment whenever concomitant therapies or conditions affecting absorption change.
Some specific causes have characteristic complications. With amiodarone, thyroid status may influence arrhythmia control and cardiac function, making therapeutic balance particularly delicate. With lithium, hypothyroidism may worsen depressive symptoms and reduce energy and concentration, affecting psychiatric stability and adherence. With immunotherapies and targeted therapies, thyroid dysfunction may occur within a broader spectrum of endocrine and systemic adverse effects. Hypothyroidism may therefore coexist with other endocrinopathies or organ toxicities, requiring an integrated multidisciplinary approach.
Overall, iatrogenic and medication-induced hypothyroidism is a paradigm of endocrine disease in which quality of care depends on the ability to anticipate risk, perform targeted monitoring, and intervene early, transforming a potential adverse event into a manageable and stable long-term condition.