Pet therapy and animal-assisted interventions in depression

Article written and reviewed by Dr Luca Moretti

The colloquial term pet therapy includes very different interventions and, in the Italian healthcare setting, it is preferable to use the official term Animal-Assisted Interventions (AAI). The Italian national guidelines approved by the State-Regions Agreement of March 25, 2015 distinguish Animal-Assisted Therapy (AAT), Animal-Assisted Education (AAE) and Animal-Assisted Activities (AAA). Only AAT is a therapeutic intervention with defined clinical objectives, included in an individualized project and delivered by a multidisciplinary team; the simple presence of an animal, pet ownership or a recreational visit is not equivalent to therapy.

In depression, evidence is concentrated mainly in older adults, institutionalized people, patients with dementia or other psychiatric disorders, and short-duration programs. Recent meta-analyses suggest a reduction in depressive symptoms in some populations, but the quality and generalizability of the evidence are limited by small samples, substantial intervention heterogeneity, difficulty with blinding and inconsistent results. AAI can therefore be considered complementary interventions in selected settings, not a general substitute for psychotherapy, pharmacotherapy or other validated treatments.

AAT, AAE and AAA: essential clinical differences

Animal-Assisted Therapy has therapeutic and rehabilitative purposes, requires a prescription or indication consistent with the healthcare pathway, and includes measurable objectives. The animal is part of a clinical setting involving healthcare professionals and specialists in working with the species involved. The project must define indication, methods, duration, outcomes, responsibilities and discontinuation criteria.

Animal-Assisted Education has educational aims and can support relational skills, autonomy or inclusion, but should not be presented as treatment for a depressive episode. Animal-Assisted Activities have mainly recreational, social or well-being goals and can be organized in healthcare, social or community settings. Even when they reduce distress or improve mood, the nature of the intervention remains different from therapy.

Terminology in international studies does not always map directly onto the Italian classification. Terms such as animal-assisted therapy, animal-assisted intervention, animal-assisted activity or dog-assisted intervention have been used with varying definitions. This terminological uncertainty contributes to meta-analytic heterogeneity and makes it necessary to check who delivered the intervention, which animal was involved, what activities were performed and which outcomes were predefined.

Rationale and possible mechanisms

Structured contact with an animal may increase social engagement, motivation, physical activity and opportunities for communication. For a person with depression, interacting with an animal may provide a concrete, nonjudgmental stimulus, facilitate movement out of isolation and create a routine of simple tasks. In this sense, part of the effect may overlap with behavioral activation, relational support and reduction of loneliness.

Psychophysiological mechanisms have also been proposed, including modulation of the autonomic nervous system, stress reduction and changes in oxytocin or cortisol. These observations are interesting but do not demonstrate a specific antidepressant pathway. Hormonal responses depend on context and relationship and are not biomarkers that can be used to select patients or measure clinical efficacy.

In older adults with cognitive impairment, the animal may function as a multisensory stimulus, facilitate conversation and environmental orientation, and encourage participation in motor tasks. However, depression in dementia, apathy, agitation and quality of life are distinct domains: improvement in one should not automatically be interpreted as efficacy in the others.

A large part of the observed effect may also derive from nonspecific but clinically important components: increased activity, daily structure, contact with staff, sensory stimulation, a sense of competence and opportunities for social interaction. These elements make it difficult to isolate an animal-specific effect in trials and explain why comparators should control for time, attention and activity. The hypothesis of reduced isolation and behavioral anhedonia is plausible especially in institutional settings, but there is no single biological mechanism or biomarker capable of predicting who will respond. The rationale therefore remains biopsychosocial and context-dependent.

Evidence in depression

Earlier systematic reviews found generally favorable but methodologically fragile results. The meta-analysis by Souter and Miller suggested an effect on depression measures, whereas subsequent reviews highlighted the need to standardize definitions and protocols. The review of randomized trials by Kamioka and colleagues showed that the field included very different populations and interventions, preventing simple conclusions about effect size.

In older adults, a 2024 meta-analysis observed a moderate effect of animal-assisted interventions on reducing depressive symptoms, with more consistent results for some dog-assisted interventions than robotic interventions. This finding is clinically interesting but mainly concerns older populations and does not demonstrate equivalent efficacy in major depression among younger or middle-aged adults.

In patients with dementia results are more inconsistent. Trials in residential facilities, including those by Majić and Olsen, reported improvements in some depressive or behavioral outcomes, but the Cochrane review rated the evidence as insufficient or low certainty for many outcomes. The natural course of dementia, heterogeneity of scales, presence of behavioral symptoms and difficulty distinguishing depression, apathy and emotional reactivity complicate interpretation.

Overall, the evidence supports the possibility of symptomatic and relational benefit, especially in geriatric and institutional settings, but does not justify defining AAI as first-line antidepressant treatment. When depression meets diagnostic criteria for a major depressive disorder, specific therapy should be determined according to severity, comorbidities and guidelines, with AAI used as a possible adjunctive component.

Patient selection and planning

The indication should begin with a clinical assessment. It is necessary to define whether the goal is to reduce isolation, increase activity, improve participation, facilitate communication, support rehabilitation or modify a measurable depressive outcome. Preference for animals is relevant but not sufficient: previous experiences, fears, allergies, cultural or religious beliefs, cognitive abilities, fall risk, impulsivity and the ability to respect the animal must be considered.

The project should select the species and individual animal according to the objective, not simply availability. Dogs are the most studied species in many programs but are not universally appropriate. Interventions involving horses, small animals or other species have different characteristics and risks. The animal must be selected and prepared for the setting, undergo veterinary and behavioral assessment, and be protected from workloads and interactions that could compromise its welfare.

Outcomes should be defined before the intervention and measured with appropriate instruments. A “pleasant” session is not equivalent to an antidepressant response. In AAT for depression, it may be useful to combine symptom scales with measures of functioning, participation, social isolation, quality of life and behavioral observations, distinguishing the immediate effect from any sustained benefit over time.

Patient safety

AAI involves specific physical and infectious risks. Allergies and asthma may be aggravated by fur, dander or other allergens; bites and scratches, although uncommon in well-managed programs, cannot be excluded; larger animals may contribute to falls or injuries. Zoonoses are a preventable but real risk, particularly important in immunocompromised or very frail patients or those with invasive devices.

Prevention requires hand hygiene, veterinary monitoring, protocols for cleaning and access to clinical areas, temporary exclusion of animals showing signs of illness, assessment of patient skin lesions and attention to multidrug-resistant organisms in healthcare settings. Not all wards are suitable for the same type of intervention, and local policies must be consistent with infectious risk.

There are also psychological risks. Phobia, grief after the loss of a previous animal, traumatic experiences, disgust or social pressure may make the interaction negative. Consent must be genuine, and patients must be able to refuse or stop the activity without consequences. In patients with severe agitation, unpredictable behavior or marked impulse-control difficulties, the safety of the animal and staff must have the same priority as potential therapeutic benefit.

Animal welfare and professional quality

An ethically appropriate AAI is based on dual protection: human benefit does not justify animal stress or suffering. Behavioral signs of stress, avoidance, fear or fatigue must be recognized by staff; session duration and frequency must be compatible with the individual characteristics of the animal. Selection cannot be based solely on obedience but should include temperament, recovery capacity, health and response to the clinical setting.

• The animal must undergo appropriate veterinary assessment and behavioral assessment.
• The patient must have an indication and goals consistent with the type of AAI.
• Allergies, zoonoses, falls, bites, scratches and phobias must be assessed before the intervention.
• The session should be stopped if significant distress develops in the patient or signs of stress appear in the animal.

The quality of an AAI also requires protection of the animal as a participant in the intervention. Selection, health and behavioral suitability, working times, breaks, the ability to withdraw and recognition of stress signals must be managed by competent professionals, with veterinary supervision according to the model established by national guidelines. An animal that is tired, frightened or forced to interact reduces clinical quality and increases the risk of incidents. Animal welfare is therefore not an optional element but a condition of safety and appropriateness, together with hygiene, traceability, team training and documentation of therapeutic objectives.

Role in depression and limitations

Animal-assisted interventions may be valuable as a complementary component of care, especially when the goal is to reduce isolation, increase participation or support older and frail people. Evidence for reducing depressive symptoms is promising but not sufficiently consistent to consider these interventions equivalent to established antidepressant treatments.

The choice should be individualized and benefit verified over time. There is no reason to offer AAI to people who do not want contact with animals or to use the popularity of “pet therapy” as scientific justification. Quality depends on correct classification of the intervention, team competence, animal protection, risk management and measurement of clinically relevant outcomes.

When used, AAT should have endpoints consistent with the project: symptom reduction, increased participation, reduced isolation or improvement in specific functions, assessed with appropriate clinical and observational tools. Benefit should be interpreted in the context of overall treatment and the natural history of depression. There are no data allowing AAI to be considered equivalent to validated psychotherapies, antidepressants or neuromodulation techniques in major depressive disorders. Their value lies mainly in being a personalized complementary intervention, potentially useful for selected patients and settings but not generalizable to anyone who likes animals.

Bibliography
1. Villarreal-Zegarra D et al. Effectiveness of animal-assisted therapy and pet-robot interventions in reducing depressive symptoms among older adults: A systematic review and meta-analysis. Complementary Therapies in Medicine. 80, 2024: 103023.
2. Kamioka H et al. Effectiveness of animal-assisted therapy: A systematic review of randomized controlled trials. Complementary Therapies in Medicine. 22(2), 2014: 371-390.
3. Charry-Sánchez JD et al. Animal-assisted therapy in adults: A systematic review. Complementary Therapies in Clinical Practice. 32, 2018: 169-180.
4. Bert F et al. Animal assisted intervention: A systematic review of benefits and risks. European Journal of Integrative Medicine. 8(5), 2016: 695-706.
5. Chang SJ et al. Animal-Assisted Therapy as an Intervention for Older Adults: A Systematic Review and Meta-Analysis to Guide Evidence-Based Practice. Worldviews on Evidence-Based Nursing. 18(1), 2021: 60-67.
6. Lai NM et al. Animal-assisted therapy for dementia. Cochrane Database of Systematic Reviews. 2019(11), 2019: CD013243.
7. Moretti F et al. Pet therapy in elderly patients with mental illness. Psychogeriatrics. 11(2), 2011: 125-129.
8. Majić T et al. Animal-Assisted Therapy and Agitation and Depression in Nursing Home Residents with Dementia: A Matched Case-Control Trial. American Journal of Geriatric Psychiatry. 21(11), 2013: 1052-1059.
9. Olsen C et al. Effect of animal-assisted interventions on depression, agitation and quality of life in nursing home residents suffering from cognitive impairment or dementia: a cluster randomized controlled trial. International Journal of Geriatric Psychiatry. 31(12), 2016: 1312-1321.
10. Souter MA et al. Do animal-assisted activities effectively treat depression? A meta-analysis. Anthrozoös. 20(2), 2007: 167-180.
11. Santaniello A et al. Methodological and Terminological Issues in Animal-Assisted Interventions: An Umbrella Review of Systematic Reviews. Animals. 10(5), 2020: 759.
12. Winkle M et al. Dog Welfare, Well-Being and Behavior: Considerations for Selection, Evaluation and Suitability for Animal-Assisted Therapy. Animals. 10(11), 2020: 2188.