Table of contents
Some medicines make you put on weight. Most often these are antipsychotics, especially olanzapine and clozapine, some antidepressants and anti-epileptic medicines, glucocorticoids, and insulin and some diabetes medicines. You should not stop a medicine like this on your own, because stopping treatment suddenly can cause withdrawal symptoms or a relapse of the illness and, after steroids, adrenal insufficiency. If you are putting on weight because of a medicine, you need to see the doctor who prescribed it. They can change the dose or the medicine, and obesity can be treated at the same time, without stopping the medicine.
In brief
- If a medicine is making you gain weight, do not stop taking it on your own. Any change to the dose or the medicine is decided by the doctor who prescribed it, and that doctor works out how to reduce it safely.
- Among antipsychotics, olanzapine and clozapine have a particularly large effect on body weight. After at least 48 weeks of treatment with olanzapine, body weight increased by 7% or more in 64 out of 100 patients, and by 25% or more in one in eight.
- Write down your weight before treatment and weigh yourself every week. In a study of people taking psychotropic medicines, gaining more than 5% in the first month predicted large weight gain after a year.
- Obesity can be treated without stopping a psychiatric medicine, including with a medicine licensed to treat obesity. The doctor chooses it taking into account the other medicines you take because, for example, naltrexone with bupropion has contraindications that apply to many people receiving psychiatric or addiction treatment.
Can you stop taking a medicine yourself if it makes you gain weight?
No. Stopping or switching such a medicine needs to be agreed with the doctor who prescribed it. Many antidepressants, antipsychotics, anti-epileptic medicines and steroids are stopped gradually, because stopping treatment suddenly can cause withdrawal symptoms or bring on a relapse sooner.
Overweight and obesity that appeared after starting a medicine can be treated even while you continue to take the same medicine. If you stop the medicine on your own, on the other hand, the depression, psychosis or epileptic seizures it was prescribed for may come back. If you have already stopped taking the medicine, tell the doctor treating you as soon as possible, even if you feel well.
What are the risks of suddenly stopping a psychiatric medicine or a steroid?
The official product information describes what can happen if treatment is stopped suddenly and gives the minimum period over which the dose should be reduced. The tapering schedule is set by the doctor treating you. It depends on the dose, the length of treatment, the illness and how you tolerate each reduction, so for some people it takes much longer than this minimum.
| Medicine (example) | What can happen if it is stopped suddenly | Minimum period over which the dose is reduced (the schedule is set by the doctor) |
|---|---|---|
| Sertraline (antidepressant) | Withdrawal symptoms, most often dizziness and disturbances of sensation and sleep. In studies, they occurred in 23% of people who stopped treatment and in 12% of those who continued it (4) | At least 1 to 2 weeks, and depending on how the patient responds, even several months |
| Venlafaxine (antidepressant) | Withdrawal symptoms, common especially after stopping suddenly | At least 1 to 2 weeks, in some people several months or longer (5) |
| Quetiapine (antipsychotic) | Insomnia, nausea, headache, diarrhoea, vomiting, dizziness and irritability | At least 1 to 2 weeks (6) |
| Pregabalin (anti-epileptic, painkiller and anti-anxiety medicine) | Insomnia, headache, nausea, anxiety, depression, suicidal thoughts, seizures | At least a week (7) |
| Lithium (mood stabiliser) | Earlier return of the symptoms of the illness, which gradual withdrawal may delay | At least 2 weeks (8) |
| Prednisone, e.g. Encorton (glucocorticoid) | Adrenal insufficiency. This risk does not apply to a course shorter than 7 days at a dose of up to 40 mg a day (9) | The schedule depends on the illness, the dose, the length of treatment and the patient's response |
Which medicines cause weight gain?
The most weight is usually gained on certain antipsychotics, especially olanzapine and clozapine. Some antidepressants, anti-epileptic medicines and mood stabilisers, glucocorticoids, and insulin and some diabetes medicines also increase body weight. There are large differences between medicines in the same group, and not everyone gains weight on the same medicine.
We put together the risk ratings in the table based on the studies cited and the official product information. This is only a rough classification, and the risk for an individual is assessed by a doctor.
| Medicines | Risk of weight gain (our summary) | What studies showed |
|---|---|---|
| Antipsychotics: olanzapine, clozapine | High | In a comparison of 18 antipsychotics in studies lasting several weeks in people with schizophrenia, olanzapine and clozapine had the most unfavourable effects on body weight, blood sugar and blood fats (2). After at least 48 weeks on olanzapine, body weight increased by 7% or more in 64% of patients and by 15% or more in 32% (10) |
| Antipsychotics: quetiapine, risperidone | Moderate | Depending on the dose, quetiapine increased body weight by 0.8 to 1.4 kg in studies lasting 3 to 8 weeks, compared with 0.2 kg on placebo, mostly in the first weeks of treatment (6). Risperidone increased body weight by 0.8 kg more than placebo (1) |
| Antidepressants: mirtazapine, amitriptyline | Moderate | Increased weight and appetite are very common side effects of mirtazapine, affecting at least 1 in 10 people (11). In studies, mirtazapine increased body weight by 1.5 kg more than placebo, and amitriptyline by 1.8 kg more than placebo (1) |
| SSRI and SNRI antidepressants: escitalopram, paroxetine, duloxetine, venlafaxine, citalopram, sertraline | Usually small | In a US observational study of more than 180,000 people starting treatment, the differences in body weight between these medicines after six months were at most 0.4 kg, although data on who actually continued treatment were incomplete (12). In a UK observational study of almost 300,000 people, weight gain of at least 5% was 21% more common in people taking any antidepressant than in those not taking one, and the higher risk persisted for at least 6 years. Both studies are observational, and the authors of the UK study point out that the link may not be causal (13) |
| Anti-epileptic medicines and mood stabilisers: valproic acid, pregabalin, gabapentin, lithium | Moderate | With valproate and pregabalin, weight gain is common, meaning it affects 1 to 10 in 100 people (14, 7). Gabapentin increased body weight by 2.2 kg more than placebo (1). People on lithium gained weight more often than on placebo, but less often than on olanzapine (15) |
| Glucocorticoid tablets: prednisone, methylprednisolone | Depends on the dose and length of treatment | Increased appetite, weight gain, water retention and changes in how body fat is distributed (9). People with rheumatoid arthritis who took at least 5 mg of prednisone a day, or an equivalent dose of another steroid, for more than six months reported weight gain more often than those not taking steroids (16) |
| Diabetes medicines: insulin, sulfonylureas (e.g. glimepiride, gliclazide), pioglitazone | Moderate | Sulfonylureas and pioglitazone increased body weight by 1.8 to 2.8 kg more than placebo (1). Insulin also promotes weight gain. Among diabetes medicines, metformin and GLP-1 medicines reduce body weight |
| Blood pressure medicines and antihistamines (for allergies) | Uncertain | Placebo-controlled studies did not show a statistically significant change in body weight or were based on very low-quality evidence (1) |
Why do some medicines make you gain weight?
Many of these medicines increase appetite. Increased appetite is a known side effect of olanzapine, quetiapine, mirtazapine, pregabalin and prednisone (10, 6, 11, 7, 9). Steroids also make the body retain water and change how body fat is distributed. For insulin, sulfonylureas and pioglitazone, the guidelines of the Polish Society for the Treatment of Obesity (PTLO) list increased appetite, fat storage and water retention (3). When insulin lowers blood sugar, the body stops losing sugar in the urine, and with it calories. Some people with diabetes also eat more for fear of hypoglycaemia (low blood sugar) or after having had an episode (17).
Body weight is also affected by the illness itself and by how treatment goes. In studies of antipsychotics, people whose symptoms improved more usually gained more weight (2). Depression itself can also make you put on weight, especially atypical depression, even when it is not treated (3).
How can you tell if a medicine is causing your weight gain?
A medicine is the likely cause if your weight gain started within a few weeks or months of starting treatment or increasing the dose, especially if your appetite has also increased. This is why it helps to have a record of your weight before treatment and the dates of all changes to your medicines.
Body weight also changes for other reasons, and several of them can overlap. In someone who stops drinking or smoking and starts an antidepressant at the same time, it is hard to tell where the extra kilograms are coming from without a record of measurements. We describe how weight changes in these situations in our articles on weight gain after quitting smoking and on weight after you stop drinking. The cause may also be the menopause or an underactive thyroid (hypothyroidism), which a doctor checks for when weight gain is unexplained, for example with a TSH test. We have gathered other reasons why your weight may go up despite dieting in our article on what to check when you cannot lose weight.
When should you see a doctor about weight gain from a medicine?
Ideally straight away, if your weight goes up noticeably after you start a medicine or increase the dose. With psychiatric medicines, an important warning sign is a gain of more than 5% in the first month, which means more than 4 kg from a starting weight of 80 kg. In a Swiss study of 351 patients who started psychotropic medicines that promote weight gain, such early gain was the best predictor that body weight might go up by 20% or more after a year. In people who gained 5% or less in the first month, weight gain in the following months was usually moderate (18).
How should you monitor your weight after starting a new medicine?
Weigh yourself before the first dose of a new medicine, then once a week at the same time of day, and measure your waist once a month. With olanzapine, body weight should be checked before treatment, after 4, 8 and 12 weeks and then every three months, and blood sugar should be tested before treatment, after 12 weeks and once a year (10). PTLO also recommends close monitoring of body weight after starting antidepressant treatment (3). We explain what blood sugar, lipid profile and liver function test results mean in our article on tests before obesity treatment.
Which symptoms alongside weight gain on a medicine need a prompt appointment?
Olanzapine and quetiapine can raise blood sugar and sometimes cause diabetes or make it worse (6, 10). If, as well as gaining weight, you develop severe thirst, frequently pass large amounts of urine, feel unusually hungry and feel weak, you need to have your blood sugar checked quickly and contact a doctor. In rare cases, very high blood sugar leads to ketoacidosis or coma, so increasing drowsiness or confusion alongside these symptoms needs urgent medical help.
You should also see a doctor without delay if your weight is rising quickly and you have also developed swelling in your legs, breathlessness or marked weakness. With steroids, this may mean water retention, but the cause may also be another illness that needs urgent investigation.
What can a doctor do if a medicine is making you gain weight?
The doctor who prescribed the medicine has several options: to reduce the dose, to switch to another medicine with less effect on body weight, to add a medicine that limits weight gain, or to keep the current treatment and refer the patient for obesity treatment. The choice depends above all on how well the current medicine controls the illness.
The PTLO guidelines recommend that, where possible, people who have to take medicines that promote weight gain should be prescribed the medicine with the least effect on body weight (3). Among antidepressants, anti-epileptic medicines and antipsychotics, there are some that in studies increased body weight only slightly, did not change it or reduced it (1, 2). The authors of the comparison of antipsychotics stress, however, that the medicine has to be chosen to suit the clinical situation and the preferences of the individual patient.
Switching medicines does not always lead to a clear reduction in body weight. A Cochrane review included 4 studies with 636 people with schizophrenia or related disorders. In two studies involving 287 people, average body weight after switching from olanzapine to aripiprazole or quetiapine was slightly lower than in people who stayed on olanzapine, but the difference was not statistically significant. Mental state did not differ significantly between people who switched and those who stayed on olanzapine, but there were few studies and they usually lasted no longer than six months (19). A medicine that controls symptoms well cannot always be replaced with another, so the decision to switch is made by the treating doctor together with the patient.
What should you prepare before talking to your doctor about weight gain from a medicine?
- The names and doses of all the medicines you take, with the date you started each one and the dates of any dose changes
- Your weight before treatment and now, ideally with a record of weekly measurements
- Your waist measurement and recent results for blood sugar, glycated haemoglobin and lipid profile, if these tests have been done
- Information about changes in your appetite and sleep, and about drinking alcohol and smoking
- Questions: is there a medicine with less effect on body weight, what might happen to my symptoms after a switch, and can my obesity be treated without changing my current medicine?
We write about what else to bring to your first appointment and what the doctor will ask in our guide on where to start obesity treatment.
How is obesity treated if you need to keep taking a psychiatric medicine?
In the same way as in other people: with changes to eating, physical activity, psychological support and, if the criteria are met, an obesity medicine. PTLO recommends considering medicines licensed for obesity treatment in people with obesity who take antipsychotics. According to the guidelines, working on habits soon after an antipsychotic is started may also help (3).
A review of 95 studies covered almost 5,900 people with schizophrenia and related disorders who were taking antipsychotics. The GLP-1 medicines studied reduced body weight by about 3 to 11 kg more than placebo. The certainty of these results was rated as moderate, although for each of these medicines there were only 2 or 3 studies (20). With liraglutide at the dose used to treat obesity (Saxenda), however, there is a caveat: its efficacy and safety have not been established in people taking medicines that can cause weight gain, and it is not recommended in this group (21).
In the obesity treatment programme at Nasz Gabinet, the doctor diagnoses obesity based on BMI and waist circumference, assesses blood tests and decides on eligibility for medication according to PTLO criteria. According to the guidelines, contraindications and the risk of interactions must always be ruled out before starting an obesity medicine, so it is a good idea to prepare a list of all your medicines with their doses for the consultation. You keep taking your psychiatric medicine unless the psychiatrist treating you decides to change it. If a patient's drinking is hazardous, we also refer them to our addiction treatment clinic at the same time.
When can't naltrexone with bupropion (Mysimba) be used?
Naltrexone combined with bupropion is an obesity medicine in tablet form. It must not be used in the following situations, among others (22):
- in bipolar disorder, including if it was diagnosed in the past
- in epilepsy or if you have had seizures in the past
- in bulimia or anorexia, now or in the past
- in people dependent on opioids, including those treated with methadone or buprenorphine
- in the period immediately after a dependent person suddenly stops drinking alcohol or taking benzodiazepines
- in people who take bupropion or naltrexone for another reason, for example naltrexone to treat alcoholism
- less than 14 days after stopping an MAO inhibitor
The risk of seizures on this medicine also increases with alcohol misuse and when antipsychotics or antidepressants are taken at the same time. Bupropion slows the breakdown of some of them, including paroxetine and risperidone, so the doctor chooses their dose carefully. Since the medicine came onto the market, there have also been reports of suicidal thoughts and behaviour, so the patient needs to be watched closely, especially at the start of treatment and after every dose change (22).
Do hormonal contraception and HRT cause weight gain?
Studies do not confirm that combined contraceptive pills or menopausal hormone therapy (HRT) noticeably increase body weight. Greater weight gain was seen in some studies with the contraceptive injection containing medroxyprogesterone.
A Cochrane review covered 49 studies of combined contraception. Four of them had a comparison group not using hormones, and none showed that the pill or the patch changes body weight. The authors concluded that the data do not completely rule out an effect, but they do not suggest that it is large (23). With progestogen-only contraception (the mini-pill, hormonal coil, implant or injection), average weight gain after 6 or 12 months was less than 2 kg in most studies and usually did not differ from that in the comparison groups. In one observational study, women using the medroxyprogesterone injection gained 1.3 kg after a year and 3.5 kg after 4 years, compared with 0.2 and 1.9 kg in women with a copper coil. The review authors rated the quality of these data as low (24). If you suspect your contraception is making you gain weight, you can discuss another method with a gynaecologist. Stopping contraception without switching to another method puts you at risk of an unplanned pregnancy.
In 22 randomised trials, women using menopausal hormone therapy (oestrogen alone or oestrogen with a progestogen) did not gain more weight than those given placebo or no treatment. This is, however, an old review, covering studies published up to 1998 (25). PTLO notes the beneficial effect of this therapy on body fat distribution but does not recommend it for treating abdominal obesity (3).
Frequently asked questions
Will I lose weight if I stop or change my medicine?
There is no way of knowing in advance. In small studies, people who switched from olanzapine to aripiprazole or quetiapine had a slightly lower average body weight than those who stayed on olanzapine, but the difference was not statistically significant. Obesity that has already developed is therefore treated like any other obesity, and you should not stop a medicine as an experiment without your doctor's agreement.
Do allergy and blood pressure medicines cause weight gain?
In a review of 257 placebo-controlled studies, the results for blood pressure medicines and antihistamines did not show a statistically significant change in body weight or were based on very low-quality evidence. The studies therefore do not settle this question. If you gain weight while taking such medicines, discuss both the medicine and other possible causes with your doctor.
Will a doctor prescribe an obesity medicine if you gained weight because of other medicines?
Yes, if you meet the same criteria as other people with obesity: a BMI of at least 30, or at least 27 with a weight-related condition such as high blood pressure or prediabetes, and changes to eating and physical activity alone have not been enough (3). Which obesity medicine the doctor can suggest depends on the medicines you take. We describe the criteria in more detail in our article on eligibility for obesity medicines.
Do GLP-1 medicines increase the risk of suicidal thoughts?
In 2024, the European Medicines Agency reviewed data on suicidal thoughts and behaviour in people taking GLP-1 medicines, including semaglutide and liraglutide. It concluded that the available data do not support a causal link (26). Any change in mood during obesity treatment should nevertheless be reported to a doctor, and someone being treated for depression should also tell their psychiatrist about the obesity medicine.
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Gaining weight on a medicine you cannot stop taking?
In our 6-month online programme, the doctor decides whether you are eligible for medication according to PTLO criteria, and in video consultations you talk to a doctor and a psychologist. Every month, the doctor reviews your treatment based on the measurements you enter in the app.
