A meta-analysis of 15 observational studies found a two-way association: people with obesity more often subsequently developed depression, and people with depression more often developed obesity. Depression can contribute to weight gain through appetite, sleep and activity changes, but not everyone gains weight. We ask about mood at the initial consultation and at check-ups. Screening tools such as the Beck Depression Inventory can help when depression is suspected; diagnosis requires clinical assessment. Obesity and depression can be treated alongside one another.
Some psychiatric medicines increase appetite and weight. The table draws on a 2020 meta-analysis of 100 trials involving 25,952 people with schizophrenia and a 2010 review of 116 antidepressant studies. It describes average associations, not a prediction for an individual.
| Medicine or group | Effect on body weight | Our approach |
|---|
Clozapine, olanzapine | High metabolic risk. In the meta-analysis, clozapine was associated with about 3 kg more weight gain than placebo and olanzapine with about a 1-point BMI increase; median trial duration was 6 weeks. | Monitor weight, glucose and lipids, coordinate with the psychiatrist and assess obesity medication eligibility separately. |
Quetiapine, risperidone | Moderate average effect; weight change depends on the person and treatment duration. | Regularly assess weight and treatment benefits and discuss any medication change with the psychiatrist. |
Aripiprazole, haloperidol, lurasidone | A smaller average effect than some other antipsychotics, but weight-gain risk is not zero. | Assess the possible contribution of medication and other causes of weight gain. |
Amitriptyline, mirtazapine, paroxetine | Greater tendency to weight gain than some other antidepressants; the course varies individually. | Monitor weight and discuss alternatives with the psychiatrist when health permits. |
Other SSRIs (selective serotonin reuptake inhibitors) and venlafaxine | Effects vary by medicine and treatment duration; changes may occur before a year has passed. | Monitor from the start rather than assume everyone follows the same course. |
Bupropion, fluoxetine | Some studies found weight loss; with fluoxetine, mainly in the short term. | Do not combine Mysimba with another bupropion product, as this duplicates the active substance. |
What we do when a patient gains weight on psychiatric medication and cannot stop it
If olanzapine or clozapine controls the psychiatric illness, maintaining it may be the priority. We coordinate the plan with the psychiatrist and assess obesity medication eligibility separately. In a 2017 trial, 103 people with schizophrenia taking clozapine or olanzapine, with overweight or obesity and prediabetes, received liraglutide 1.8 mg daily or placebo for 16 weeks. The between-group weight-change difference was 5.3 kg in favour of liraglutide; normal glucose tolerance was achieved by 63.8% versus 16%. Psychotic symptoms did not worsen in this trial. However, this was not the Saxenda 3 mg regimen: Saxenda's product information does not recommend its use for obesity secondary to weight-increasing medicines or eating disorders. The trial does not establish automatic eligibility for Saxenda.
Newer semaglutide trials are also available. In HISTORI, published in 2025, 154 people with schizophrenia, prediabetes and BMI of at least 27 taking second-generation antipsychotics received semaglutide up to 1 mg weekly or placebo for 30 weeks. The between-group weight-change difference was 9.21 kg in favour of semaglutide. This finding applies to that population, dose and duration; it cannot automatically be extended to tirzepatide.
Metformin is another option a doctor may consider. A meta-analysis of 20 trials with 1,070 participants found a mean weight difference of about 3.3 kg in its favour versus placebo for antipsychotic-associated weight gain. This is an off-label use. The doctor assesses the rationale, kidney function and tolerability and coordinates with the treating specialist.
How is binge-eating disorder treated?
Episodes involve eating a large amount in a short time, a sense of losing control and marked distress. At least one episode a week for 3 months is one diagnostic criterion, but it is not sufficient on its own. Other features include the absence of regular compensatory behaviours such as induced vomiting or fasting. A US population survey of 9,282 people conducted from 2001 to 2003, using the diagnostic criteria of that time, found lifetime prevalence of 3.5% in women and 2% in men. These are not Poznań population figures.
Obesity medicines may help control appetite but do not replace eating-disorder treatment. For adults, NICE recommends cognitive behavioural guided self-help with professional support. If unsuitable or ineffective after 4 weeks, group eating-disorder-focused CBT is an option, with individual therapy when a group is unavailable or declined. Medical, dietary and psychotherapeutic care is arranged according to needs and availability. A history of anorexia or bulimia is a contraindication to Mysimba.
Can obesity medicines worsen mood or cause suicidal thoughts?
In April 2024, the EMA concluded that available evidence did not support a causal link between suicidal thoughts or self-harm and semaglutide, liraglutide, dulaglutide, exenatide or lixisenatide. That assessment did not include tirzepatide and does not guarantee that mood can never worsen.
Mysimba contains the antidepressant bupropion and requires monitoring, especially at the start and after dose changes. The antidepressant warning includes the risk of suicidal behaviour in people under 25. Depression alone is not an automatic contraindication, but the condition, medicines and interactions need assessment. Contraindications include a history of bipolar disorder or seizures, acute alcohol or benzodiazepine withdrawal and taking another bupropion or naltrexone product. MAO inhibitors and serotonergic medicines must also be checked. New agitation, insomnia or worsening mood needs prompt medical contact. An immediate risk of suicide requires urgent medical help.