Not a day in my practice goes by without a patient complaining about their weight gain. So often the antidepressants are blamed. The simple answer is that weight is a straightforward mathematical calculation: you can only gain weight if you consume more kilojoules than what you burn, and vice versa. But is it really so simple?

Seeking help for depression is the first, courageous, and important step to recovery. However, being compliant with treatment (i.e. taking medication regularly, addressing stressors, attending therapy, and following a healthy lifestyle) is not always easy. Even if you do feel better, medication often does have side-effects – some only mildly bothersome, but others can be more distressing such as weight gain.


Non-compliance with treatment may have weighty consequences: being depressed impairs personal well-being, interpersonal relationships, socio-occupational functioning, and quality of life. Being overweight increases the risk of obesity-related illnesses such as diabetes mellitus, hypertension, ischaemic heart disease, osteoarthritis, lower back pain, infertility, sleep apnoea, strokes, and even cancer.


There is a complex relationship between depression, antidepressant medication and weight gain. Clinical findings have suggested that obesity may double the risk of developing depression and vice versa. The hypothylamic-pituitary-adrenal (HPA) axis is activated during stress, and also dysregulated in obesity and metabolic syndrome. This is the most well-understood shared common pathophysiological pathway with depression. Inflammation is another pathway that links obesity to depression: both disorders are associated with the activation of cytokines in the inflammatory pathways. Increased leptin and insulin resistance, frequently observed in obesity and in pro-inflammatory states, may also induce alterations in the brain and increase the risk of depression.


“You should choose whether you want to be happy or fat” is a hurtful, and completely irrelevant remark! For those dealing with depression, this can be a very sensitive subject since body weight is very closely tied to self-esteem and associated levels of depression. Up to 25% of people on antidepressant medication complains about weight gain, but tablets contain (virtually) no kilojoules! Although weight gain doesn’t occur with every drug or for every person, when it does happen, it can be a significant problem that we shouldn’t just ignore. So why do people gain weight?


The effect of depression

One of the symptoms of depression is a change in appetite. While two-thirds of individuals with depression initially present with weight loss, some may experience an increased appetite with carbohydrate craving (the “emotional eaters”). Increased body weight in the early phases of treatment may therefore be due to successful treatment (i.e. a return of appetite), or persisting symptoms due to suboptimal treatment (i.e. the increased appetite have not normalised).


Depression is also associated with low energy levels, and lack of motivation and drive. People often stop exercising or really struggle to start exercising. This contributes to a lowered metabolism – and putting people at risk for weight gain.


Sleep-deprivation, either due to insomnia associated with depression, or poor sleeping habits (including late-night snacking) reduces leptin levels (the chemical that makes you feel full), and increases ghrelin (the hunger-stimulating hormone). Some studies have shown that people who sleep less than seven hours a day may be more likely to be overweight than those who get nine hours of sleep or more. However, if you sleep too much, you will also not burn enough kilojoules!


The effect of antidepressants

There are a number of theories as to why antidepressants contributes to weight gain. Successful treatment for depression helps people to rediscover pleasure in their lives – including food. People may therefore be overeating without even realising it!  There is also evidence that some antidepressant drugs may induce a variable amount of weight gain, but results are sparse and often contradictory. However, comprehensive reviews and pooled results from studies showed that only amitriptyline, mirtazapine, and paroxetine were associated with a greater risk of weight gain. In contrast, some weight loss occurs with fluoxetine and bupropion, although the effect of fluoxetine appears to be limited to the acute phase of treatment. Other medications have no transient or negligible effect on body weight in the short term. The effect of each antidepressant may vary greatly depending on an individual’s characteristics and generally became more evident with long term treatment.


Other culprits

Although most people put on weight because they eat and drink more kilojoules than they burn through everyday activities, in some cases, weight gain may be due to an underlying health condition such as:

  • An underactive thyroid. Without enough thyroid hormone, the body’s metabolism slows down, which can lead to weight gain.
  • Diabetes treatment. People with longstanding diabetes often eat a diet that “matches” their insulin dose with excessive snacking to prevent a hypoglycaemic incident. This contributes to excessive kilojoule intake and weight gain.
  • Ageing: As people get older, they begin to lose modest amounts of muscle due to inactivity. Muscles are an efficient kilojoule burner: losing muscle weight slows your metabolism.
  • Steroid treatment. Cortisone is used to treat a variety of conditions, such as asthma, arthritis, and systemic lupus. Long-term use seems to increase appetite and fluid retention in some people, leading to weight gain.
  • Cushing’s syndrome. Cushing’s syndrome, a rare condition in which you are exposed to too much of the stress hormone cortisol (either due to steroid treatment, adrenal over activity, or a tumour) may also cause weight gain – most prominent around the face, neck, upper back, or waist.
  • Fluid retention. Fluid retention (oedema) is not uncommon – for example when one is premenstrual. However, more severe retention may be indicative of kidney or heart problems.
  • Polycystic ovary syndrome (PCOS). PCOS, a common hormonal problem, affects ovarian function, and increases insulin and testosterone levels. This can cause irregular menstruation, infertility, excess hair growth, acne and weight gain.
  • Contraception. Contrary to popular belief, combination birth control pills aren’t proven to cause lasting weight gain. Some women may experience some weight gain related to fluid retention, but this is usually short-term.
  • Menopause. Most women do gain some weight (especially around the waist) around the time of menopause. This is due to hormonal changes, a slowing of metabolism due to ageing, and changes in lifestyle and activity levels.
  • Quitting smoking. Quitting smoking is one of the best things you can do for your health. When you quit, you may gain some weight, but perhaps less than you think. On average, people who stop smoking gain less than 4kg. Weight gain is often due to increased snacking as an activity to replace smoking.
  • Other medications. Several other prescription drugs are linked to weight gain. Medication such as antipsychotic drugs (used to treat disorders like schizophrenia and bipolar disorder), migraine treatment, anti-epilepsy drugs, and high blood pressure tablets may contribute to weight gain.


What should you do?

If you gain weight after starting an antidepressant, discuss the medication’s benefits and side effects with your doctor. If the benefits outweigh the side effect of weight gain, consider managing your weight by eating healthier and getting more physical activity while enjoying an improved mood due to the medication. Try the following:

  • A healthy, balanced diet. Be careful of severe restriction which affects brain chemistry in a negative way. The sense of deprivation can also contribute to feelings of depression. Be careful of “banting”. Recent studies have shown that the combination of stress and antidepressants followed by long-term high-fat diets, long after discontinuation of the medication, can result in markedly increased weight – in excess of what is caused by a high fat diet alone. Severe carbohydrate restriction can also cause a drop in tryptophan – a precursor of melatonin (which helps with sleep) and serotonin (which is already “low” in depression and anxiety disorders). Consult a dietitian!
  • Regular exercise. Exercise does not only benefit your weight and physical health, but also reduces symptoms of anxiety and depression, improves your concentration, and promotes a sense of self-control. The ideal is to exercise at least 30min per day, at least five times a week. Even if you don’t lose weight immediately, you can begin controlling the gain. Get moving!
  • Get a hobby. If you know you’re an emotional eater, you need to find other forms of distraction, such as a hobby, calling a friend, going for a walk or having a soothing bath.
  • Switch antidepressants. Discuss with your doctor the possibility of adjusting the dose of your medication, or to switch the medication. Medications such as paroxetine, amitriptyline, imipramine, mirtazapine, and phenelzine (which binds with histaminergic receptors and interacts with hunger and satiety hormones) are more prone to weight gain, and a switch to SSRIs (such as fluoxetine and sertraline), an SNRI (such as venlafaxine), an NDRI (buproprion), a SARI (trazodone) or newer medications such as agomelatine or vortioxetine may be beneficial. However, the neurochemistry involved in depression is extremely complex and slightly different for everybody, so while switching drugs may help with the weight gain, you might forfeit some control over the symptoms of depression.
  • Cognitive Behavioural Therapy (CBT). Eating habits can be changed through identifying lifestyle behaviours to be modified, setting goals, modifying triggers of excessive eating, and reinforcing desired behaviour with CBT. Gradual but consistent behaviour change leads to healthier eating habits, exercise, and weight loss of up to 0.7kg per week!


The use of weight loss drugs is in general NOT a good idea. These drugs can often cause anxiety and insomnia, and weight loss is not sustainable – the weight is often regained as soon as you stop using the drugs. Never use any weight loss medication, not even herbal products, without discussing it with your psychiatrist.