Throughout my career as a dietitian I have come across many patients struggling with weight and uncertainty around medications. The association with weight gain can cause some patients to refrain from taking their medications, which can seriously affect their outcomes and health. The intention of this article is to both further explain the issue, and also to offer some solutions from a Dietitian ’s perspective.


Mental health research has been expanding in the last decade. Researchers are more aware of interactions between brain and body and whether they are positive or negative. A study conducted on patients with depression found that those taking drugs to ameliorate their mental health were 21% more likely to gain weight than the control group. Antidepressants such as Mirtazapine were more heavily associated with a larger amount of weight gain. This specific type of medication is not used as a first line method of treatment; however, it is still frequently used as an alternative or adjunct where initial therapies have not been entirely successful. When patients are prescribed this drug, medical professionals highlight this predominant side effect.


This particular study at King’s College London shows an association between antidepressants and weight gain, which perhaps suggests that all anti-depressants directly cause an increase in weight. However, weight gain is actually more highly correlated with patients’ lifestyles and/or eating habits. The symptoms of depression are varied across a large spectrum, and some patients experience a loss of appetite due to their emotional condition. When they start to recover, their appetite increases, and consequentially they tend to put on weight. On the other side of the spectrum, some patients tend to eat more as a result of their depressive state, which results in weight gain at the start of treatment.


Of the specific medications, Fluoxetine, a known selective serotonin reuptake inhibitor (SSRI) has been suggested to alter the patient’s weight, either provoking an increase or decrease. Serotonin is a neurotransmitter that regulates anxiety, mood and appetite, and SSRIs inhibit the reuptake of serotonin, leading to higher levels in the brain. An imbalance can cause cravings for specific foods, often those rich in carbohydrate. In terms of the link between weight gain and anti-depressants, it can really be considered a “chicken and egg” situation. A decrease in serotonin in the brain can cause changes in appetite, however, regulating this imbalance with SSRIs could also cause changes in weight. Thus, it is more a case of the increase in appetite, rather than the drug itself directly causing the weight gain as a result of the medication dosage.


Research2 also suggests that SSRIs may provoke weight loss when taken in short-term, yet weight gain when taken long-term. Paroxetine is the anti-depressant SSRI most likely to lead to weight gain, whereas Sertraline is the least likely. However, environment also appears to play a part in the management of weight whilst taking the medication. In a 2017 study, researchers observed that those patients who were gaining weight whilst on antidepressants were also practicing “unhealthy habits” such as eating a Western diet consisting of highly processed foods, lacking in physical exercise and frequently using tobacco.


Antidepressant medication causing weight gain is one of main concerns of patients, and can cause them to stop taking their medications as they are worried about appearance and health. This in turn can exacerbate the depressive systems.

It is difficult to state with ultimate confidence that weight gain is a cause of antidepressant intake, as there is limited evidence to determine the direct link between both variables. In terms of the changes in weight, the science is more thoroughly explained by the imbalance in the neurotransmitter directly involved in depression. Due to the fact that serotonin involves so many different systems and networks in the body, it is inevitable that these changes wouldn’t be present with the neurotransmitter’s alteration.

Serotonin is heavily involved in a range of different systems in the body. It plays an important role in mood, social behaviour, appetite, digestion, sexual desire and memory. Its role in coordinating basic system functions is therefore a desirable target for antidepressant medication. However, when one neurotransmitter spans across this range of networks, it is almost impossible to not target all the system outputs when attempting to resolve one of the symptoms of the condition. A basic analogy used to understand how serotonin affects the entire system is to think of mould on bread. Mould spreads, and while you can remove the one causing the mould, all the others will still be affected as the fungus is still present within the conditions inside the bag. Treating one slice at a time will still spread the mould to other slices.


It is important to remember that the way we put on weight is by having excess calories in our diet, and medication itself has too few calories to directly cause weight gain. However, when medication causes cravings of high carbohydrate and sugary foods, such as confectionaries, chips, crisps, and large portions of starch at mealtimes, there are some tips I can offer, from the perspective of a Dietitian .


One is to go for the high fibre variety of carbohydrates, as they can fill you up for a greater length of time, as well as tending to have more nutrition than refined options. So instead of a chocolate bar, try a granola bar, which may only have slightly fewer calories than a chocolate bar, but can be higher in protein and fibre, and therefore make you feel full for longer.

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If the issue is a craving for something sweet, try a piece of fruit. This might be around 60kcals, as compared to confectionary options, which commonly have between 150-250kcals per portion.

Next, when portioning out your meals try to keep to only a quarter of a plate of starchy foods, or use a measuring cup and have no more than ¾ cup of potato (or one medium baked potato or sweet potato), or half a cup of whole grain rice. If you are making homemade oven baked potato wedges then use a medium potato as a portion for each person. And psychologically, the more wedges you cut out from it, the bigger the portion will look.


Lastly, if you are craving something chocolatey, which is a common scenario, try a chi seed pudding with stevia, cacao powder, and either skimmed milk or a plant based alternative such as almond or oat milk. The chi seeds will go gelatinous and form a sweet but guilt free, nutritious pudding, low in calories, and high in fibre and protein, as well as calcium and other vitamins and minerals.


Still on the topic of weight management, it is also worth mentioning another area that has gained attention in terms of its links to weight gain, the category comprised of antipsychotics. The British Association for Pharmacology suggests that the predominant weight gain window is within the first 6 months of taking such medications. Commonly used antipsychotics like Haloperidol and Quetiapine are known for having either low or medium risks of weight gain, and some sources even dictate that Haloperidol is associated with a relatively high risk of weight gain and obesity. However, research and results are limited in this field 3 and there is no immediate causation between antipsychotic dose and weight gain.


Psychosis is a disorder caused by an imbalance in the chemistry of the brain, and the neurotransmitters responsible for behaviour, mood and emotions. These neurotransmitters include dopamine, serotonin, noradrenaline and acetylcholine. Through the alteration of these different chemicals using antipsychotics, specific thoughts, hallucinations, delusions and mood swings can be prevented or suppressed. However, once again, by attempting to target a problem that is caused by a range of symptoms belonging to many different networks, there are bound to be underlying side effects involved.


Research4 suggests that changes in appetite and food intake, as well as delayed satiety signalling whilst intaking antipsychotics, are to be expected. Antipsychotics may play a role in insulin resistance and glucose dysregulation. As psychosis affects so many different systems within the brain and body, targets for these drugs are likely to affect a variety of systems rather than just one in particular.


Unlike antidepressants, antipsychotics can cause increased glucose and lipid levels in the blood, and all patients will require regular monitoring of their HbA1c and lipids. Patients who have diabetes are required to have frequent monitoring when taking antipsychotics, as the medication could give rise to further impairment in the glucose mechanism, resulting in increased abdominal adiposity (overweight, obesoity).


Regarding adiposity, the Journal of the American Medical Association investigated the adverse changes in adiposity and insulin sensitivity amongst patients prescribed antipsychotic medication. Patients aged 6-18 who were diagnosed with a psychiatric disorder were randomly assigned different antipsychotic medications, which included: aripiprazole, olanzapine or risperidone. Later, these patients were measured for their total body fat percentage, and for insulin sensitivity in muscles. Abdominal adiposity was measured using magnetic resonance imaging. Regarding the results, from baseline to week 12 of the study, total body fat percentage increased by 1.18% for Risperidone, 4.12% for Olanzapine, and 1.66% for Aripiprazole. Regarding the subcutaneous fat, there was a significant increase in patients taking Olanzapine compared to Risperidone and Aripiprazole. In terms of the bigger picture, youths prescribed this type of medication would need to be supervised and monitored for any changes in their cardiometabolic system.5


Here, again, it’s important for the patient to have education and support with their nutrition, and help to prevent weight gain, which can worsen diabetic control and be a direct cause of higher glucose levels.

Meals and snacks must be low in sugar and refined carbohydrates, and be replaced with high fibre, low processed foods. Ensure that portions of carbohydrate are not too large, and protein is eaten alongside the carbohydrates, in order to help slow down the absorption of sugars. Good examples are peanut butter on toast, cheese and crackers, cheese with apples.

Fruit is a healthy snack, although care needs to be taken as fruit contains its own sugars, and eating a large amount of fruit in one go (fruit salads) can over-increase blood sugars. A good rule of thumb is that a portion is roughly a fist size. Fruit juice is a tricky one, being packed full of vitamins and fibre if it has the pulp, but it does contain a lot of sugar, so if desired then only have a small glass, 150ml, and add 150ml of cold water. Also, drink it with a meal so that it mixes in the stomach with other food groups (proteins, fats), which will help to slow down the sugar absorption.


In summary, it’s important to remember that medication itself does not cause weight gain, and patients should always take what is prescribed to them by their GP. The best approach to tackling weight gain is to enjoy a well-balanced meal, and to put techniques in place to maintain a neutral calorie intake.