The term nutraceuticals is used operationally for nutrients or food-derived compounds used for health purposes; herbal medicines or phytoceuticals are plant-derived preparations with biological activity. These categories are not synonymous with antidepressant efficacy and, above all, are not synonymous with harmlessness. Clinical assessment should distinguish at least three situations: correction of a documented deficiency, nutritional supplementation in a person without deficiency, and use of a compound as a true antidepressant or augmentation intervention.
The literature includes omega-3 fatty acids, folates and L-methylfolate, vitamin D, zinc, S-adenosyl-L-methionine, probiotics, Hypericum perforatum, saffron and numerous other products. The strength of evidence varies widely by molecule, formulation, dose, population and use as monotherapy or adjunctive treatment. WFSBP/CANMAT guidelines devoted to nutraceuticals and phytoceuticals recognize that some agents have useful clinical data, but they do not justify treating the entire category as equivalent to standard antidepressants or combining supplements without assessing interactions and risks.
A deficiency of a vitamin, mineral or other nutrient may contribute to neuropsychiatric symptoms and should be corrected according to the specific diagnosis. This is conceptually different from giving the same nutrient in supplemental doses to a person with adequate nutritional status in the hope of obtaining an antidepressant effect. For example, correcting a deficiency of vitamin D, folate or vitamin B12 addresses a medical indication in its own right; efficacy as a treatment for depression in people without deficiency requires separate evidence.
Assessment should therefore begin with dietary history, medications and supplements already taken, malabsorption, bariatric surgery, restrictive diet, pregnancy, kidney or liver disease, alcohol use and conditions that increase the risk of deficiencies. Laboratory tests should not be ordered indiscriminately as a “depression panel” but according to clinical indications. Once a deficiency is identified, normalization of nutritional status may be necessary even if it does not by itself produce remission of the depressive disorder.
Assessment of a possible deficiency should be guided by history, diet, comorbidities, medications, clinical signs and risk factors, not by indiscriminate testing panels. For example, vitamin B12, folate, iron or vitamin D may be relevant in specific contexts, but correction of a documented deficiency primarily addresses a nutritional or medical problem. Observational studies associating low nutrient levels with depression do not automatically establish causality: reduced appetite, low sun exposure, chronic illness and socioeconomic conditions may produce reverse causality or confounding. This distinction prevents biomarkers of vulnerability from being turned into unproven treatment indications.
Omega-3 fatty acids with long-chain components, particularly EPA and DHA, have been studied as monotherapy and especially as adjuncts to antidepressants. Meta-analyses show an average antidepressant signal but with substantial heterogeneity; formulation composition appears important, and several studies suggest more favorable results with products containing a higher proportion of EPA. This does not mean that any commercially available fish oil is equivalent to the preparations studied.
Proposed mechanisms include modulation of neuronal membranes, eicosanoids, inflammation and monoaminergic transmission, but none constitutes a clinical biomarker capable of reliably identifying responders. Use should be considered within the overall treatment context, with attention to quality, actual EPA/DHA content and product oxidation.
The most common adverse effects are gastrointestinal symptoms and a “fishy” taste or reflux. At high doses or in patients taking antithrombotic drugs, it is prudent to consider the overall bleeding risk, although usual formulations are generally well tolerated. Allergies or products of uncertain quality warrant additional caution.
Heterogeneity also concerns product composition. Studied formulations differ in the ratio of eicosapentaenoic acid (EPA) to docosahexaenoic acid (DHA), total dose, purity, duration and use as monotherapy or adjunctive treatment. Several meta-analyses have suggested more favorable signals for preparations with a high proportion of EPA, but this observation does not allow any commercial supplement to be equated with the products used in trials. Clinical decisions should consider formulation quality, possible gastrointestinal effects, bleeding risk in predisposed individuals or those treated with drugs that increase bleeding, and the absence of a universal antidepressant dose suitable for everyone.
Folate metabolism is involved in one-carbon reactions and in the synthesis of methionine and S-adenosylmethionine. L-methylfolate is the biologically active form capable of crossing the blood-brain barrier and has been studied as augmentation in patients with an insufficient response to SSRIs. Randomized trials have shown benefit with specific treatment regimens in adults with SSRI-resistant depression, but this does not justify indiscriminate folate use in every patient.
The presence of common MTHFR variants should not be interpreted as a diagnosis of “methylation deficiency” or as automatic proof that L-methylfolate is needed. Before prolonged folate supplementation, vitamin B12 status should be considered because high amounts of folate can correct megaloblastic anemia without resolving neurological injury due to B12 deficiency.
S-adenosyl-L-methionine (SAMe) participates in numerous methylation reactions and has been studied both alone and as augmentation. A randomized trial showed benefit when it was added to a serotonin reuptake inhibitor in nonresponders, but the overall literature is less extensive than for standard antidepressants. SAMe can cause gastrointestinal symptoms, insomnia or activation and should be used with particular caution in people with bipolar disorder or risk of manic switching; combinations with other serotonergic agents require clinical supervision.
St John’s wort (Hypericum perforatum, St John's wort) is one of the most extensively studied herbal medicines in depression. Systematic reviews and meta-analyses have found efficacy superior to placebo and, for some standardized extracts in mild or moderate depression, results comparable to conventional antidepressants. Generalizability is limited, however, by variability between extracts, product quality and study heterogeneity; results from a standardized preparation should not be generalized to any herbal tea or supplement.
St John’s wort is also a clear example of why “natural” does not mean free of interactions. Components such as hyperforin induce metabolic and transport systems, including CYP3A4 and P-glycoprotein, and can reduce exposure to numerous drugs. Clinically relevant interactions occur with hormonal contraceptives, anticoagulants, immunosuppressants, antiretrovirals, some antiseizure drugs, antineoplastic agents and many other therapies. Combination with serotonergic drugs can also increase the risk of serotonin toxicity.
For these reasons, St John’s wort should not be added to antidepressant therapy without medical supervision. Photosensitivity, gastrointestinal effects, agitation and mood switching in vulnerable individuals should also be considered. In severe or psychotic depression or when suicide risk is high, the evidence does not justify its use as a substitute for treatments with proven efficacy.
Saffron (Crocus sativus) has been evaluated in several small trials and meta-analyses suggesting an effect on depressive symptoms, with promising results particularly in mild or moderate forms. However, sample sizes, geographic concentration of some studies, differences between extracts and limited duration warrant caution. Larger independent trials and long-term comparisons are needed before assigning it the same degree of certainty as standard treatments.
For vitamin D the evidence is heterogeneous. Correcting a deficiency is indicated for medical reasons, whereas the antidepressant effect of supplementation in unselected populations is less consistent. Differences among studies also depend on baseline level, dose, duration and comorbidities. Excessive doses can cause hypercalcemia and kidney injury, so the idea that a vitamin can be increased indefinitely because it is “safe” is incorrect.
Zinc has been studied as an adjunct in some trials and meta-analyses, but the evidence does not justify routine high-dose use. Excessive chronic supplementation can cause copper deficiency, anemia and neurological disorders. Probiotics and microbiota-targeted interventions are an active area of research: some studies suggest small benefits for mood, but effects are strain-specific and cannot be extrapolated from one product to another. In severely immunocompromised patients, administration of live microorganisms requires particular caution.
The validity of a trial depends on the product studied. Plant extracts may differ by species, plant part, solvent, standardization, contaminants and amount of active molecules. Mineral and vitamin supplements may differ in chemical form and bioavailability. Pharmaceutical quality and correspondence between label and actual content are therefore part of efficacy and safety, not a commercial detail.
Before adding a nutraceutical, a proper medication reconciliation should be performed, including prescription drugs, over-the-counter products, herbal teas, recreational substances and other supplements. Interactions may be pharmacokinetic, pharmacodynamic or related to additive effects on coagulation, blood pressure, sedation or serotonin. Pregnancy, breastfeeding, liver disease, kidney disease and polypharmacy require a higher threshold for caution.
Nutraceuticals do not constitute a homogeneous therapeutic class. Some have sufficient evidence to be considered selective adjuncts or, in specific cases, herbal treatment options; others remain experimental or lack convincing evidence. Decisions should start from the specific substance and indication, not from the general label of “supplement.”
In patients with moderate or severe major depression, treatment-resistant depression, psychosis, catatonia or high suicide risk, use of supplements should not delay treatments with demonstrated efficacy. When a nutraceutical is used, its goal, trial duration, response parameters, possible interactions and discontinuation criteria should be defined. This approach allows evidence-supported options to be integrated without turning nutrition or herbal medicine into an indiscriminate therapeutic promise.
A rational strategy first defines the goal: correcting a deficiency, using a product with adjunctive evidence in a subgroup, or accommodating a patient preference without reducing the effectiveness of the main treatment. Each intervention should have a trial duration, a response criterion and a review of interactions and tolerability. If no benefit emerges, continuing multiple products indefinitely increases costs, complexity and interaction risk without a scientific basis. In moderate or severe depression, nutraceuticals should not delay pharmacotherapy, psychotherapy or neuromodulation when these are indicated; their role, when present, remains selective and subordinate to the level of evidence for the individual compound.
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