Can a medicine be the reason for your weight gain?
If your weight rose weeks or months after starting a medicine, it is natural to ask whether the medicine is the cause. Some medicines are known to cause weight gain, but not every rise is drug-related, and people on the same drug gain different amounts. A systematic review of 257 randomised trials (54 drugs) linked weight gain to several drugs, including amitriptyline, mirtazapine, olanzapine, quetiapine, risperidone, gabapentin, pioglitazone and several sulfonylureas [1]. For many others, including blood pressure drugs and antihistamines, the change was not statistically significant or rested on very low-quality evidence [1]. A narrative review adds long-term corticosteroids, lithium, valproate, insulin and beta-blockers [2].
Weight also changes with sleep, appetite, activity, age, hormones and conditions such as an underactive thyroid [8]. So the useful question is whether the timing and pattern fit, and what can be done safely. For another common cause, you can read our article on hypothyroidism and weight.
The first rule of this article: do not stop a medicine or change its dose on your own. Keep taking it as prescribed and discuss it with your doctor, because alternatives or adjustments may exist [7].
How can medicines lead to weight gain?
There is no single mechanism, and nobody can predict who will gain. A medicine may increase appetite, cause drowsiness that lowers movement, or make the body hold fluid. These are possible explanations, not proven mechanisms for each drug [1,2]. The illness itself also matters: depression, poorly controlled diabetes and joint pain change appetite and activity whatever the treatment [8].
Which medicine groups are known for weight gain?
This is a digest of figures from published reviews. They are averages or ranges from studies, not promises for you personally:
• Oral corticosteroids: short-term use has not shown significant change, but long-term use (3 months or more) is associated with gain: prednisone 1.7 to 5.8 kg, prednisolone 1.5 to 4.4 kg, cortisone 1.5 to 8.4 kg [2].
• Antidepressants: amitriptyline 0.4 to 7.3 kg, nortriptyline 0.3 to 4.1 kg, mirtazapine 0.4 to 2.4 kg, citalopram up to 7.1 kg in some studies, and phenelzine (9.1 kg in 6 of 14 patients in one study). The SSRIs and SNRIs fluoxetine, sertraline, venlafaxine and duloxetine are discussed in the next section [2].
• Antipsychotics and mood stabilisers: in placebo-controlled trials olanzapine 2.4 kg, quetiapine 1.1 kg, risperidone 0.8 kg [1]. The narrative review reports olanzapine 3.6 to 10.2 kg and clozapine 4.5 to 16.2 kg, lithium 1.1 to 9.9 kg and valproate 0.7 to 6.9 kg, while lamotrigine and carbamazepine are neutral or closer to weight loss [2].
• Glucose-lowering drugs: insulin 0.4 to 4.8 kg, pioglitazone 2 to 3.9 kg, chlorpropamide 2.6 to 5.3 kg, tolbutamide 1.6 to 2.8 kg [2]. In trials, glimepiride added 2.1 kg, gliclazide 1.8 kg and glyburide 2.6 kg [1]. Metformin is associated with loss of 1.0 to 2.9 kg [2].
• Beta-blockers (atenolol, propranolol, metoprolol): modest gain, usually in the first few months and then a plateau, which may not be clinically significant [2].
• Anti-epileptics: gabapentin 2.2 kg, while topiramate and zonisamide are associated with weight loss [1].
• Hormonal contraception and antihistamines: limited or low-quality evidence, covered in a later section [1,9].
Some medicines (metformin, topiramate, zonisamide) are associated with weight loss, but the choice stays with your doctor [1,2].
Do cortisone and joint medicines increase weight?
Cortisone and similar corticosteroids are often prescribed for joint disease, severe allergy and asthma. Short courses did not show a major weight change, while long-term use (3 months or more) was associated with gain [2]. Part of the early rise may be fluid, which can fluctuate and show in the face and ankles [3].
Cortisone should not be stopped suddenly after long use, because the body may need a gradual reduction planned by the doctor [3]. For other joint medicines the reviews used here report no clear weight figures, so we give none [1,2]. While on cortisone, cut back on salt and processed food, keep meals regular, include protein, and use InBody now and then to see water and fat shares [3].
Antidepressants: which add weight and which are closer to neutral?
Not all antidepressants are alike. Amitriptyline, nortriptyline, mirtazapine and phenelzine sit in the weight-gain group, and citalopram in some studies. Fluoxetine, sertraline, venlafaxine and duloxetine tend to be weight neutral, and bupropion is associated with weight loss [2]. Choosing among them is the doctor's decision based on your condition and other medicines [2,7]. Amitriptyline is sometimes prescribed in small doses for sleep or nerve pain, so ask why it was prescribed.
Depression itself can change appetite and weight, and stopping an antidepressant suddenly can cause withdrawal symptoms and relapse. Do not stop it, swap it or lower the dose yourself. The clinic does not provide psychiatric treatment, so the talk about an alternative belongs with your psychiatrist, while we help with nutrition and weight follow-up [7,8].
Anti-epileptics, mood stabilisers and antipsychotics
Among anti-epileptics, valproate and gabapentin were associated with gain, lamotrigine and carbamazepine are closer to neutral, and topiramate and zonisamide with loss [1,2]. Seizure prevention comes first, so an epilepsy medicine should never be adjusted outside your doctor's supervision.
Among antipsychotics, olanzapine and clozapine raise weight noticeably, quetiapine and risperidone less so [1,2]. Guidance expects the treating team to monitor weight and body mass index regularly, so ask for it if yours is not measured [4,6]. We build a realistic nutrition plan and follow weight and InBody, without changing any psychiatric or neurological medicine [4,8].
Diabetes medicines: insulin and tablets
Among diabetes medicines, insulin, pioglitazone and some sulfonylureas were associated with weight gain, whereas metformin was associated with a small loss [1,2]. Pioglitazone may also cause fluid retention, which the doctor monitors [5].
What matters is that high glucose is harmful in itself. So do not cut insulin or leave a tablet in order to lose weight [5].
What do we do? We review your meal schedule so it fits your medicine doses, set a suitable carbohydrate amount for each meal, and track weight and InBody. Adjusting the medicine, the dose or the type of insulin is the decision of your treating diabetes doctor, and we coordinate with them [5,8].
Blood pressure and cholesterol medicines: do they add weight?
The systematic review did not find strong evidence that blood pressure medicines raise weight in general [1]. The notable exception is beta-blockers such as atenolol, propranolol and metoprolol, with a modest gain usually in the first few months and then a plateau [2]. They are also prescribed for palpitations and migraine. The doctor may consider an alternative group, such as ACE inhibitors or angiotensin receptor blockers, which appear closer to weight neutral [2], but that decision belongs to the doctor alone [7]. Neglected high blood pressure is far more dangerous than a modest weight rise.
Cholesterol-lowering statins do not appear among the weight-gain drugs in these reviews [1,2]. If you notice ankle swelling or breathlessness with a heart or blood pressure medicine, contact your doctor promptly, because this may be fluid rather than fat [7].
Allergy medicines and hormonal contraception
Antihistamines: the systematic review found weight change either not significant or supported by very low-quality evidence [1]. Some types cause drowsiness, so movement falls, which is not the same as adding fat.
Hormonal contraception: the evidence is limited and often low quality. There is no evidence that intrauterine methods, the implant, the progestogen-only pill or combined hormonal contraception cause significant weight gain. The three-monthly injection appears associated with some gain in some women, particularly those under 18 with a body mass index of 30 or more, although the data cannot confirm cause and effect [9,10]. Women tend to gain weight over time with any method or none [9].
Do not stop your contraceptive on your own, because that may lead to an unplanned pregnancy. The clinic does not offer gynaecology, so a change of method belongs with a gynaecologist [9,10].
Fluid or fat?
Not every kilogram gained is fat. Corticosteroids especially may cause fluid retention, which can appear quickly and fluctuate day to day [3]. Medicines can also change appetite and activity, so weight alone is an insufficient indicator [2]. An InBody measurement and waist circumference show whether the rise is in fat, water or muscle. For more, read our article on water retention or weight gain.
Weigh yourself at the same time once a week and record it. If the rise is fast over days with ankle swelling or breathlessness, arrange a medical review promptly, and do not stop any medicine before coordinating with your doctor [3,7].
How to tell medicine-related gain from other causes
Weight gain has many causes: an underactive thyroid [8], menopause, water retention, changes in sleep, appetite and activity, and conditions such as polycystic ovary syndrome. A rise after starting a medicine is a timing clue, not proof, and needs assessment [1]. To read more, see our article on hypothyroidism and weight, our article on menopause and weight management assessment, and our article on thyroid dose and weight.
A medicine diary and timeline
Before the visit, prepare a simple record: medicine name, dose, start date, weekly weight, and symptoms (appetite, sleep, activity, swelling, mood). Add other medicines, supplements and over-the-counter painkillers. This timeline helps the prescribing doctor see whether the rise coincides with the medicine. Bring previous test results too, if you have them [7].
Questions to ask: could my medicine contribute? Are there alternatives within the same class? Can the dose be adjusted? What follow-up is needed? [2,7]
What can you do with food and movement while staying on the medicine?
If changing the medicine is not possible, lifestyle becomes your main tool, and guidance advises reviewing any other medicines that may be adding weight [7]. These steps do not conflict with any medicine:
• Regular meals with protein and fibre, so a raised appetite does not lead to repeated snacking. • Less processed food, pickles and salt, especially with medicines that hold fluid. • Fewer sweetened drinks and juices. • Light resistance exercise and daily movement according to your ability. • Enough sleep.
Check with your doctor that any exercise or new diet suits your condition and medicines [8]. Avoid harsh crash diets, which can upset glucose, blood pressure or medicine balance.
Never stop or change a medicine on your own
Do not stop, skip, restart or change the dose of any medicine without speaking to the doctor who prescribed it. The benefit, such as controlling glucose, blood pressure, a mental health condition or seizures, may outweigh the risk of weight gain [2,7].
Alternatives may exist within the same class, for example fluoxetine or sertraline instead of amitriptyline, lamotrigine instead of valproate, or ACE inhibitors instead of beta-blockers; dose adjustments may also help [2]. These are examples from the reviews, not advice to act on yourself. Stopping suddenly can be harmful, so always coordinate with the treating doctor [3,7]. NICE advises reviewing whether other medicines can be changed with specialist input, while accepting that it may not be possible [7].
Nutrition plan and InBody follow-up at the clinic
At La Rose Clinics we provide clinical nutrition and weight-management follow-up, and we do not treat endocrine, cardiac or psychiatric conditions. The decision about the medicine stays with your doctor.
An individual nutrition plan, an InBody measurement and follow-up every 4 to 8 weeks help distinguish fluid from fat and protect muscle [8]. The Maadi branch is at 14 El-Mokhtar Street, off El-Nasr Street, behind QNB, New Maadi. The Fifth Settlement branch is at CMC Medical Mall, fourth floor, North 90th Street, on Wednesdays from 3:30 pm. You stay on your medicines as your doctor prescribed [7].
Read also: the booking page
A monitoring plan
A monitoring plan that brings your prescribing doctor and nutrition together: • Weight once a week at the same time [8]. • InBody every 4 to 8 weeks [8]. • Medicine review with your doctor [7]. • Tests when needed, such as glucose and lipids, as your doctor advises [5].
When to book
Book a nutrition and weight-management consultation if: • you notice a marked weight rise after starting a new medicine [8]. • you notice swelling with a quick rise on the scale, after ruling out a need for urgent medical assessment [3]. • you want a preventive plan with weight and InBody monitoring [7].
If concerning symptoms appear, such as breathlessness, high fever or severe pain, seek urgent assessment before a routine booking [7]. Use the booking page and mention your current medicines. We will not change your medicine; we build an eating and follow-up plan around what your doctor prescribes.
