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Antipsychotics and weight gain

Some antipsychotic medicines used to treat mental illnesses may cause weight gain.

Most weight gain due to taking antipsychotics happens in the first six weeks of treatment. It's easier to prevent this than to try to lose the weight at a later stage.

Weight gain can make you more at risk of developing diabetes as well as many other medical conditions such as heart disease and high cholesterol.

Causes of weight gain from antipsychotics

Mental illness itself, or the side-effects of medication, may mean you have less energy and are less active than usual, making it harder to maintain your weight.

Some antipsychotic medications can make you feel hungrier, so you eat more. You might also crave sweet or fatty food.

Monitoring weight gain from antipsychotics

You should weigh yourself every two weeks to monitor your weight.

Your mental health team or general practice team will measure your height, weight and blood pressure regularly.

You'll also have regular blood tests to monitor your blood glucose and cholesterol levels.

Preventing weight gain from antipsychotics

Eating well along with keeping physically active can help you maintain your weight. Having regular meals, watching your portion sizes and cutting down on foods and drinks rich in sugar and fat are important. For more information, see Eating well for good health and keeping active.

If you need to lose weight, How to lose weight has information about how to do this.

Do not stop your medication without discussing this with your healthcare team.

Metformin for losing weight and preventing weight gain

Metformin can help you lose weight if you've already put it on. It can also help you keep the weight off if your mental health team thinks you're at a high risk of gaining weight when you start an antipsychotic.

If you start taking metformin at the same time as your antipsychotic, you may only need to take it for the first six to eight weeks of treatment. But if the metformin is working for you, your healthcare team may prescribe it for longer.

You'll start taking a small dose of metformin with your main meal. This may be gradually increased to one tablet with breakfast, lunch and dinner.

Getting help with weight gain

Your general practice team or mental health team may refer you to a dietitian or a healthy lifestyle and cooking programme such as Puāwai-Kai.

There are several groups that can help you with increasing your physical activity.

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Written by HealthInfo clinical advisers. Page created September 2023.

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