Yes. Some medicines used for mental health conditions can contribute to weight gain, although the effect varies considerably from one medicine and one person to another. Antidepressants, antipsychotics and mood stabilisers can all be associated with weight changes in some people. Weight gain after starting treatment does not automatically prove that the medicine is the cause, because appetite, activity levels, sleep, the underlying condition and other health factors may also play a role.
If you have noticed a change in your weight since starting or changing treatment, the timing and pattern can help your doctor or pharmacist assess what may be happening. Do not stop a prescription medicine or change the dose on your own because of weight gain. For more information about other possible symptoms, see the mental health medication side-effect symptoms guide and the main Mental Health Medication Side Effects hub.
How mental Health Medication Weight Gain can be linked to medicines or supplements
Medicine-related weight gain can happen for several different reasons.
Some medicines can increase appetite or make you feel hungry more often. Others may cause tiredness or sleepiness, which can indirectly reduce your usual level of physical activity. Certain antipsychotic medicines can also affect blood sugar, blood fats and other aspects of metabolism, which is one reason physical-health monitoring is important during treatment.
With antidepressants, the picture can be more complicated. Weight gain may sometimes be a medicine side effect, but improved appetite as depression improves can also contribute. Changes in eating habits, activity levels and ageing can affect weight at the same time, so the cause is not always straightforward.
Timing clues
A medicine may be worth discussing as a possible contributor if:
- your weight started increasing after you began a new medicine;
- the change followed a dose increase or treatment change;
- you have also noticed increased hunger, cravings or changes in eating patterns;
- you feel more sleepy or less physically active than before;
- your healthcare team has noticed changes in your blood sugar, cholesterol or triglycerides; or
- the medicine’s professional information or patient leaflet lists weight gain or increased appetite as a possible side effect.
Timing is useful information, but it cannot confirm the cause by itself. Thyroid problems, fluid retention, hormonal changes, changes in mental health, other medicines and lifestyle factors can also affect body weight.
Medicines and product categories that may be associated with this symptom
Antipsychotic medicines
Weight gain is a recognised possible effect of antipsychotic treatment. The likelihood is not the same with every antipsychotic, and individual responses vary.
Some antipsychotics, particularly olanzapine and clozapine, have a stronger association with weight gain and metabolic changes than some alternatives. Risperidone and quetiapine can also be associated with weight gain.
Because antipsychotic medicines can affect more than body weight, healthcare teams may monitor measurements such as weight, waist circumference, blood pressure, blood glucose and blood fats.
If you are gaining weight while an antipsychotic is otherwise controlling important mental health symptoms, the decision about what to do next needs to balance both benefits and risks. This is a discussion to have with the prescribing clinician rather than a reason to stop treatment yourself.
Antidepressants
Weight gain can occur with antidepressants, but people respond differently. Some people gain weight, others notice little change, and the same medicine may affect two people very differently.
Mirtazapine, for example, can increase appetite and is associated with weight gain in some people. Some tricyclic antidepressants and certain other antidepressants are also more strongly associated with weight gain than others.
If weight gain is becoming difficult to manage, a doctor can review the overall treatment plan and the benefits and side effects of the medicine.
Mood stabilisers
Weight gain can also occur with some medicines used as mood stabilisers.
Long-term lithium treatment may be associated with weight gain. Lithium can also affect thyroid and kidney function, so people taking it require appropriate monitoring. An underactive thyroid can itself cause symptoms including tiredness and weight gain.
Sodium valproate or valproic acid can also cause weight gain in some people, and weight monitoring may form part of ongoing treatment.
Other medicines and supplements
Mental health medicines are not always the only products involved. Other prescription medicines, over-the-counter products, herbal preparations and supplements may affect appetite, fluid balance, sleep or interact with treatment.
Tell your doctor or pharmacist about everything you are taking, including supplements, vitamins and herbal products. Do not assume that a product is risk-free simply because it is described as “natural”.
Red flags: when this symptom may need urgent medical attention
Gradual weight gain by itself is usually not a medical emergency. However, some symptoms occurring alongside a change in weight need faster assessment.
Seek urgent medical help if you develop difficulty breathing, swelling of your face, lips, tongue or throat, fainting, or a severe blistering or peeling rash. These can be signs of a serious allergic reaction.
You should also obtain prompt medical advice if weight gain is rapid and accompanied by swelling of the hands or ankles, shortness of breath, marked changes in urination or other significant new symptoms. With medicines such as lithium, kidney or thyroid problems need to be considered when relevant symptoms occur.
People taking certain antipsychotics should also be aware of possible signs of very high blood sugar. For example, olanzapine can be associated with hyperglycaemia. Extreme thirst, frequent urination, extreme hunger, blurred vision or unusual weakness should be reported promptly to a healthcare professional.
If you take lithium, symptoms such as repeated vomiting or diarrhoea, worsening tremor, muscle weakness, severe drowsiness, confusion, poor coordination, blurred vision or difficulty speaking can indicate lithium toxicity and require urgent medical assessment.
The correct warning signs depend on the medicine you take. Check the patient information leaflet supplied with your medicine and seek professional advice if you develop a severe, unusual or rapidly worsening symptom.
What to track before speaking to a doctor or pharmacist
A simple record can make it easier to work out whether there is a pattern.
What to track
Consider noting:
- the name of each prescription medicine, over-the-counter product and supplement you use;
- when each medicine was started;
- any recent dose changes;
- when you first noticed the weight change;
- weight measurements taken under reasonably consistent conditions;
- changes in appetite, hunger or cravings;
- changes in sleep or daytime sleepiness;
- changes in your normal activity level;
- swelling of the hands, feet or ankles;
- unusual thirst or changes in urination;
- other new side effects;
- major changes in diet, stress or daily routine; and
- whether the medicine is helping the condition it was prescribed to treat.
Try to focus on the trend rather than reacting to normal day-to-day fluctuations.
A doctor or pharmacist may also want to review your blood pressure or arrange tests such as blood glucose, cholesterol, thyroid function or other investigations depending on the medicine and your individual circumstances.
What not to do without medical advice
Do not stop mental health medication suddenly
Do not abruptly stop an antidepressant, antipsychotic, mood stabiliser or other prescription mental health medicine because you are worried about weight gain.
Stopping treatment suddenly can cause withdrawal symptoms with some medicines and may allow the condition being treated to return or worsen. Antidepressant guidance, for example, specifically advises discussing troublesome side effects with the prescriber instead of reducing the dose or stopping treatment independently.
Do not change your dose yourself
Taking less medicine does not necessarily solve the problem and could make treatment ineffective. Any dose change should be discussed with the prescriber.
Do not switch medicines on your own
Some medicines have different effects on weight, but they also differ in effectiveness, interactions and other side effects. A medicine that appears more favourable for weight may not necessarily be the best treatment for your particular condition.
Avoid unproven weight-loss products
Do not automatically add slimming products, herbal remedies or supplements to counter medicine-related weight gain. These products can have their own side effects or interact with prescription treatment.
If weight changes are affecting your physical health, confidence or willingness to continue treatment, tell your healthcare professional. Those concerns are a legitimate part of reviewing whether a treatment remains suitable.
Related side-effect guides and reporting options in South Africa
If you are unsure whether another symptom could be related to treatment, browse the side effect symptoms A–Z guide or read more about medication side effects.
You can also speak to a doctor or pharmacist about whether your weight change is a suspected adverse drug reaction and whether further monitoring is appropriate.
In South Africa, suspected adverse drug reactions can be reported to the South African Health Products Regulatory Authority (SAHPRA). Members of the public as well as healthcare professionals can report suspected reactions through SAHPRA’s Med Safety system. Reporting a suspected side effect does not require you to prove that the medicine caused it.
See the guide on how to report side effects in South Africa for the local reporting route.
Frequently asked questions
Is weight gain a common side effect of mental health medication?
It depends on the medicine. Weight gain is a recognised side effect of several antipsychotics, some antidepressants and some mood stabilisers, but the likelihood and amount of weight change vary between medicines and between individuals. Some people experience no meaningful weight change at all.
How long can medication-related weight gain last?
There is no single timeframe. Some changes may appear relatively soon after treatment starts, while others develop during longer-term treatment. The pattern depends on the medicine, dose, individual response and other health and lifestyle factors.
If your weight continues to rise or the change is significant for you, ask your doctor or pharmacist to review it rather than waiting indefinitely.
Should I stop the medicine if I am gaining weight?
Not without professional advice. Sudden discontinuation can create additional problems, including withdrawal symptoms or worsening of the condition being treated. Speak to the prescriber about the weight change and the overall balance between treatment benefits and side effects.
When should I seek help?
Arrange a review with your doctor or pharmacist if weight gain is persistent, substantial, upsetting to you or accompanied by increased appetite, excessive thirst, changes in urination, swelling or other new symptoms.
Seek urgent medical help for trouble breathing, swelling of the face or throat, fainting, severe allergic symptoms, severe confusion, seizures, or other rapidly worsening symptoms. Anyone taking lithium who develops symptoms suggesting lithium toxicity needs urgent medical assessment.
A practical next step
If you think a mental health medicine may be contributing to weight gain, record when the change began, note any associated symptoms and take an up-to-date list of your medicines and supplements to your doctor or pharmacist.
The goal is not simply to look at the number on the scale. Your healthcare professional can consider the medicine’s benefits, the pattern of weight change, possible alternative causes and whether monitoring or changes to your treatment plan are appropriate.
Medical disclaimer: This information is for general education and does not diagnose a condition or replace advice from a doctor, pharmacist or other qualified healthcare professional. Do not start, stop, switch or change the dose of prescription medicine without professional guidance. Seek urgent medical help for severe, rapidly worsening or potentially life-threatening symptoms.