for better mental health

Antipsychotics

Explains what antipsychotics are used for, how the medication works, possible side effects and information about withdrawal.

What side effects can antipsychotics cause?

Every antipsychotic has its own possible side effects. Not everyone who takes antipsychotics will experience side effects, but many people do.

This page lists the most serious side effects that are possible with any antipsychotic drug. Some of these side effects are rare.

Certain types of antipsychotic may also have other side effects which aren’t listed here. The British National Formulary (BNF) has an A-Z list of drugs licensed for use in the UK. This list has links to find out more information about each drug, including information about side effects.

See our page on coping with side effects for guidance on what to do if you experience one of these side effects.

Antimuscarinic effects

Antimuscarinic effects are side effects caused by changes to the level of the chemical acetylcholine in your body. These effects are sometimes called anticholinergic effects.

If your level of acetylcholine changes, this can have effects all over your body. These effects include:

  • blurred vision
  • confusion and agitation
  • constipation, which may become life-threatening if not treated
  • difficulty urinating
  • drowsiness
  • dry mouth, which can cause tooth decay in the long term
  • erectile dysfunction
  • hallucinations
  • hot or dry skin, and decreased sweating
  • increased pressure in the eye
  • low blood pressure (taking hot baths increases this risk)
  • nausea (feeling sick)
  • rapid heartbeat and disturbed heart rhythm.

Antimuscarinic effects are more common with some antipsychotics than others. In particular, clozapine may be more likely to cause severe constipation than other types of antipsychotic.

These effects can also happen with other types of medication, such as tricyclic antidepressants and anti-Parkinson's drugs.

"With haloperidol my tongue hung out of my mouth and my lips were stretched wide and open. Quietiapine made me feel stoned initially, with huge weight gain."

Bed-wetting

Bed-wetting can be a side effect of antipsychotics. It is more common with some antipsychotics than others.

Blood disorders

Certain blood disorders can be a side effect of antipsychotics. These include:

  • agranulocytosis
  • blood clotting disorders
  • reduced white blood cells.

Agranulocytosis

Agranulocytosis is a blood disorder which involves the loss of one type of white blood cell. It means that you are more likely to catch infections and less able to fight them. It is very serious and people have been known to die from it.

If you have the following symptoms, it may be a sign that your immune system is not working as well as it should:

  • sore throats
  • mouth ulcers
  • a fever or chills.

If you experience these symptoms, you should contact your doctor straight away.

The risk of agranulocytosis is higher with clozapine than with other antipsychotics. If you take clozapine, you will have your blood tested regularly to check for this.

Blood clotting disorders (venous thromboembolism or VTE)

These include deep vein thrombosis (DVT) and pulmonary thrombosis (blood clot in the lung), which can be life-threatening.

Reduced white blood cells

Taking antipsychotics may cause a reduction in your white blood cells.

Body temperature problems

Antipsychotics can cause problems with regulating your body temperature. It may become too high or too low, both of which can make you feel unwell.

Emotional effects

Antipsychotics can sometimes make you feel:

  • anxious
  • excitable
  • agitated
  • aggressive
  • depressed (although some antipsychotics may have an antidepressant effect, making you feel less depressed)
  • restless and unable to keep still
  • out of touch with reality
  • socially withdrawn and detached from those around you.

Eye problems

Certain antipsychotics may cause various eye problems. These include:

  • blurred vision and difficulty reading
  • a build-up of granular deposits in the cornea and lens. This doesn’t usually affect your vision
  • degeneration of the retina, which is the light-sensitive part of the eye. This can affect your vision
  • glaucoma, which is a serious eye condition
  • oculogyric crisis, which affects the muscles that control your eye movements. It can cause your eyes to turn suddenly, so you can’t control where you look.

All antipsychotics also have the potential to cause narrow-angle glaucoma. This is a medical emergency. If you've ever had glaucoma or eye problems, you should be very cautious about taking antipsychotic drugs. You may want to avoid certain antipsychotics completely, especially those with antimuscarinic effects.

If you’re concerned about this, you can speak to your doctor or psychiatrist to find out more.

Heart problems

Antipsychotics may cause certain heart problems, such as:

  • increased heart rate
  • heart palpitations, which are heartbeats that suddenly become more noticeable in your chest
  • effects on your heart rhythm. This has been known to cause sudden death in extreme cases. The risk of this is especially linked to being on a high dose, or taking more than one antipsychotic at the same time.

See our pages on taking antipsychotics safely and dosage of antipsychotics for more information on the risks of heart problems with antipsychotics. This includes information on how you can manage these risks.

Liver disorders

Certain antipsychotics may cause liver disorders and jaundice (yellow skin).

Metabolic syndrome

Metabolic syndrome is the medical name for a combination of the following symptoms:

  • weight gain and obesity
  • high blood sugar
  • diabetes
  • high blood pressure
  • high cholesterol.

You don’t have to experience all of these symptoms to be diagnosed with metabolic syndrome. 

Taking antipsychotics can increase your risk of developing metabolic syndrome. If you experiencing metabolic syndrome, this means you are at higher risk of developing:

  • diabetes
  • stroke
  • heart disease.

This risk of this is increased even more if you have an unhealthy lifestyle. Your doctors may suggest trying to eat a healthier diet and get enough physical activity can help to reduce this risk. 

See our pages on food and mood for healthy eating tips, and physical activity and your mental health for lots of ways to get more active. If you have a difficult relationship with food and eating, our pages on eating problems may help.

You will also need to have regular health checks before and during your treatment. See our page on taking antipsychotics safely for more information.

Neuroleptic malignant syndrome (NMS)

NMS is a rare but serious neurological disorder, which means it affects your nervous system.

It can happen as a side effect of taking antipsychotics. It may also occur as a withdrawal symptom if you stop taking antipsychotics. If it does occur, it usually develops rapidly over 24 to 72 hours.

The symptoms are:

  • sweating or fever, with a high temperature
  • tremor (shaking), rigidity (feeling stiff and unable to move your muscles) or loss of movement
  • difficulty speaking and swallowing
  • rapid heartbeat, very rapid breathing and changes in blood pressure
  • changes in consciousness, including confusion and lethargy, stupor or coma.

High temperature and rigidity are usually the first symptoms to appear. This means NMS can sometimes be confused with an infection. But NMS can be very dangerous if it’s not detected and treated. In rare cases, it can be fatal.

If you’re worried that you may have symptoms of NMS, you should contact your GP urgently or call 999 for an ambulance.

What's the treatment for NMS?

If you experience NMS, the treatment is most likely to involve admitting you to hospital, stopping your antipsychotic medication and reducing your fever.

Some other methods of treatment are used, although the evidence for the use of these is not as strong. These methods may include using:

The symptoms may last for days, or even weeks, after coming off the antipsychotic that's causing them. Many people who have had NMS once go on to get it again.

If you experience NMS, you should only take antipsychotics afterwards if they are essential for your mental health. And you should have the lowest dosage possible that still gives the positive effects.

Neuromuscular side effects

Antipsychotics interfere with the brain chemical dopamine, which is important in controlling movement. Antipsychotics may therefore cause movement disorders. These are most common with first generation (older) antipsychotics and less likely with the newer antipsychotics. They include the following:

Parkinsonism

Some neuromuscular side effects are similar to the effects of Parkinson’s disease, which is caused by the loss of dopamine. These effects are known as Parkinsonism, and they include the following:

  • Your muscles become stiff and weak.
  • You find it more difficult to make facial expressions.
  • Certain small movements feel difficult, such as writing or picking up objects with your hands.
  • You develop a slow tremor (shaking), especially in your hands.
  • Your fingers move as if you are rolling a small object between them.
  • When walking, you lean forward, take small steps and find it difficult to start and stop.
  • Your mouth hangs open, and you dribble.

Loss of movement

You may find it difficult to move and your muscles may feel very weak.

Having little energy to move is also a symptom of depression, so if you experience this your doctor or psychiatrist may ask if you’re feeling depressed.

Akathisia (restlessness)

Akathisia is a feeling of restlessness that can affect your body and your emotions. For example, you might:

  • feel intensely restless and unable to sit still
  • rock from foot to foot, shuffle your legs, cross or swing your legs repeatedly, or continuously pace up and down
  • feel emotionally tense and uneasy.

Doctors might confuse these symptoms and think you are anxious or agitated. If they don't know that you have akathisia, they may suggest taking a higher dose of your antipsychotics, to help you feel calmer.

But if you have akathisia, increasing your dose of antipsychotics won’t help. So if you are diagnosed with akathisia, your doctor or psychiatrist may suggest taking another medication to reduce its effects, as well as your antipsychotic.

Muscle spasms

Muscle spasms are when a muscle in your body contracts against your control, and you cannot relax the muscle. They can be painful and may have serious effects. For example:

  • If a spasm affects the muscles of your larynx (voicebox), you may have problems with your voice. This is called dysphonia. You might find it difficult to speak normally, and people may find it hard to understand you.
  • If a spasm affects the muscles that control your eye movements, it can makes your eyes turn suddenly. It may mean you can’t control where you look. This is called an oculogyric crisis. This can feel very unpleasant. It could also be dangerous, for example if it happens while you are crossing the road or pouring boiling water from a kettle.

"I experienced twitching, stumbling and slurred speech."

Sedation (sleepiness)

Sedation, or sleepiness, is a common side effect of many antipsychotics. It is more common with certain antipsychotics than others, such as chlorpromazine and olanzapine.

Sedation can happen during the day as well as at night. So if you experience this you might find it very hard to get up in the morning. Or it might feel difficult to motivate yourself to be active during the day.

"Antipsychotics knock me out and make it very hard to function normally."

Seizures (fits)

Many antipsychotics have the potential to cause fits. If you've ever had fits in the past, you should be particularly cautious about taking antipsychotic drugs.

Sexual and hormonal problems

Many antipsychotics can cause an increase in your prolactin level. Prolactin is a sex hormone that causes the breasts to produce milk, so your levels should normally be low, unless you are  pregnant or breastfeeding.

If you have abnormally high prolactin levels, it's very common to experience some of the following sexual side effects:

Women

Women may experience:

  • vaginal dryness
  • unwanted hair
  • acne
  • loss of menstrual cycle – but this is unpredictable and your periods may return if your prolactin levels drop back down, so you could still get pregnant if you have unprotected sex

Men

Men may experience:

  • priapism (prolonged erection) – this requires urgent medical attention, so if you experience this side effect you should see your GP or go to A&E
  • spontaneous ejaculation

Both men and women

Both men and women may experience:

  • breast development and the production of breast milk
  • reduced sexual desire, difficulty becoming aroused and difficulty achieving orgasm
  • osteoporosis, which means your bones become weaker and are more likely to break

Some of the second generation (newer) antipsychotics have less effect on prolactin and produce fewer of these problems.

"Amisulpride has made my breasts grow and lactate. After having blood tests, it turns out that my prolactin levels have sky-rocketed, which is why I experienced those side effects. I am also now at risk of osteoporosis in the future."

Skin problems

Antipsychotics can cause various skin problems, for example:

  • Allergic rashes. These usually occur within the first two months of starting treatment. They usually disappear when you stop taking the drug. If you get a rash, you should contact your GP straight away to have it checked.
  • Increased sensitivity to sunlight, especially at high doses. If you're taking antipsychotics, you may need to take extra care to protect yourself from the sun.
  • A blue-grey discolouration in some skin types.

Suicidal feelings or behaviour

Some people experience suicidal thoughts and behaviours while taking antipsychotics. This can happen particularly in the early stages of taking this medication.

If you are concerned about experiencing suicidal feelings while taking antipsychotics, speak to your doctor or psychiatrist.

If you feel unable to keep yourself safe, it's a mental health emergency.

Get emergency advice

Tardive dyskinesia (TD)

Tardive dyskinesia (TD) is a side effect of certain medications, mainly antipsychotics. It involves experiencing sudden, jerky or slow twisting movements in your face or body.

See our pages on tardive dyskinesia to find out more. This includes information on what TD is, what treatments and support are available, and ways to help yourself cope.

Tardive psychosis

Tardive psychosis is a term used to describe new psychotic symptoms that begin after you have been taking antipsychotics for a while. Some scientists believe that these symptoms may be caused by your medication, not your original illness returning. The word 'tardive' means that it's a delayed effect of the medication.

This risk of tardive psychosis is one reason why it’s a good idea to withdraw slowly from your medication, if you decide to stop taking it. This is especially important if you have been taking it for a long time, as withdrawing slowly gives your brain time to readjust.

Weight gain

Weight gain is a very common side effect of many antipsychotics, particularly some of the second generation (newer) drugs. This may be because antipsychotics increase your appetite, so you want to eat more than usual. They may also cause you to become less active, for example if they make you feel very tired.

If you put on a lot of weight, this can increase your risk of developing diabetes and other physical health problems. It's also understandable if you feel upset or frustrated about these changes to your body.

If you experience weight gain, your doctor or psychiatrist may suggest switching to another antipsychotic medication. They may also suggest that you try to eat a healthy diet and increase your level of physical activity.

See our pages on food and mood for healthy eating tips, and physical activity and your mental health for lots of ways to get more active. If you have a difficult relationship with food and eating, our pages on eating problems may help.

This information was published in September 2020. We will revise it in 2023.

References are available on request. If you would like to reproduce any of this information, see our page on permissions and licensing.

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