Every antipsychotic has the potential to cause unwanted side effects. These can vary from drug to drug and from person to person – not everyone will experience side effects, but many people do. This page provides an alphabetic overview of the most serious side effects which can potentially occur with any antipsychotic drug, although some are rare.
For details of the possible side effects of a particular antipsychotic, you can look it up in our antipsychotics A–Z. For guidance on what to do if you experience a side effect, see our information on coping with side effects.
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.
Antimuscarinic effects (sometimes called anticholinergic effects) is the medical term for a group of side effects caused by changes in the level of the messenger chemical acetylcholine. This can have significant effects all over the body, including:
- blurred vision
- constipation (this may become severe enough to be life-threatening if not treated)
- difficulty urinating
- dry mouth, which can cause tooth decay in the long term
- low blood pressure, especially when getting up from sitting or lying down (taking hot baths increases this risk)
- nausea (feeling sick)
- rapid heartbeat
These effects are more common with first generation (older) antipsychotics than newer antipsychotics. They can also occur with other types of drugs; for example, they are also particularly associated with tricyclic antidepressants and anti-Parkinson's drugs.
This is more likely to occur with second generation (newer) antipsychotics.
A number of blood disorders are linked to antipsychotics:
- Reduced white blood cells.
- Agranulocytosis, 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's very serious and people have been known to die from it. The risk if agranulocytosis is mainly associated with clozapine. If you are getting sore throats or mouth ulcers, a fever or chills, these may be signs that your immune system is not working as well as it should, and you should see your doctor.
- 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.
Body temperature problems
Antipsychotics can cause you problems with regulating your body temperature. It may become too high or too low, both of which can make you feel unwell.
Antipsychotics can sometimes make you feel:
- depressed (although conversely some antipsychotics may have an antidepressant effect)
- emotionally uneasy and restless
- out of touch with reality
- socially withdrawn and detached from those around you
They can also cause you to have bizarre dreams or nightmares, which could cause you trouble sleeping.
Antipsychotics may cause various different eye problems, including:
- blurred vision and difficulty reading
- a build up of granular deposits in the cornea and lens (this doesn’t usually affect sight)
- degeneration of the retina (the light-sensitive part of the eye) – this can restrict your vision
- glaucoma (a serious eye condition)
- oculogyric crisis – this affects the muscles that control your eye movements, so your eyes may turn suddenly and you can’t control where you look
All antipsychotics also have the potential to cause narrow-angle glaucoma, which is a medical emergency. If you've ever had glaucoma or eye problems you should be particularly cautious about taking antipsychotic drugs, and it may be best to avoid certain drugs altogether – in particular some of the first generation (older) antipsychotics. You can look individual drugs up in our antipsychotics A-Z for more information.
Antipsychotics have the potential to cause:
- increased heart rate
- effects on the heart rhythm, which in extreme cases have been known to cause sudden death. This risk is particularly linked to being on a high dose and taking more than one antipsychotic at the same time.
See our pages on taking antipsychotics safely and dosage for more detail on these risks, and how to manage them.
Antipsychotics may cause liver disorders and jaundice (yellow skin). You can look individual drugs up in our antipsychotics A-Z for more information.
Metabolic syndrome is the medical term for a combination of the following symptoms:
- weight gain and obesity
- high blood sugar
- high blood pressure
- high cholesterol
You don't have to experience all these symptoms to be diagnosed with metabolic syndrome. Experiencing metabolic syndrome then puts you at higher risk of going on to develop:
- heart disease
Metabolic syndrome is thought to make you two to three times more likely to die from cardiovascular disease.
This risk is increased even further if you have an unhealthy lifestyle generally, so it's important to make sure you try to eat a healthy diet and get enough exercise. You'll 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 serious neurological disorder, meaning it affects your nervous system. It usually develops rapidly over 24–72 hours and may also occur during withdrawal from antipsychotics. The symptoms are:
- sweating or fever, with a high temperature
- tremor, 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, from lethargy and confusion to stupor or coma
As high temperature and rigidity are usually the first symptoms to appear, NMS could initially be mistaken for an infection. But NMS can be very dangerous if it’s not detected and treated, and can be fatal.
Who's most at risk of NMS?
- It mostly affects people under 40.
- It's twice as common in men as in women.
- The main trigger seems to be a change of dose within the last four to 11 days, although it can occur if you are on a steady, standard dose and have been taking it for many years.
- The risk may be higher with some of the first generation (older) antipsychotics (such as haloperidol) but all antipsychotic drugs can potentially cause NMS.
What's the treatment for NMS?
Treatment may include:
- reducing the fever
- medication to relax your muscles
- medication to counter the chemical imbalance that is thought to cause NMS
- electroconvulsive therapy (ECT) has also been used effectively
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 – so you should only take antipsychotics afterwards if they are essential, and then only at very low doses.
Neuromuscular side effects
Antipsychotics interfere with the brain chemical dopamine, which is important in controlling movement. The drugs may therefore cause movement disorders. These are most common with first generation (older) antipsychotics and less likely with the newer antipsychotics. They include:
- Parkinsonism. These effects resemble Parkinson’s disease, which is caused by the loss of dopamine. The symptoms are:
- your muscles become stiff and weak
- your face may lose its animation
- you may find fine movement difficult
- you may develop a slow tremor (shaking), especially in your hands
- your fingers may move as if you were rolling a small object between them
- when walking, you may lean forward, take small steps and find it difficult to start and stop
- your mouth may hang open and you may find that you are dribbling
- 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 may ask if you're feeling depressed).
- Akathisia (restlessness). This is more than just a physical restlessness – it can be emotional as well. You may:
Health care staff might misinterpret these symptoms to mean that you're agitated or very anxious, and suggest you need more medication to calm you down – but if you have akathisia then increasing your dose of antipsychotics won't help. Your doctor may offer to prescribe another medication on top of your antipsychotic to reduce it.
- 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
- Muscle spasms. These are acute muscle contractions that you cannot control. They may be painful and can have some serious impacts on your life. For example:
Muscle spasms are seen to particularly affect young men (although 'young' is not clearly defined in the evidence sources).
- If the problem affects the muscles of your larynx (voicebox) you may develop problems with your voice and find it difficult to speak normally (called dysphonia). This can make you feel self-conscious, and may make it hard for people to understand you.
- If the muscles that control your eye movements are affected it can makes your eyes turn suddenly, so that you can’t control where you look (called an oculogyric crisis). This can feel very unpleasant, and be disconcerting for people around you. It may 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.
All these symptoms reduce while you are asleep, so your doctor may suggest that you could avoid the worst of them (as well as feeling less sleepy during the day) if you take your medication as a single daily dose in the evening.
If you're very bothered by neuromuscular side effects, your doctor may also offer to prescribe you anti-Parkinson’s drugs to reduce the symptoms.
Sleepiness is a common side effect with antipsychotics but some, such as chlorpromazine and olanzapine, are more sedating than others. Sedation can happen throughout 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 to motivate yourself to be active during the day.
Antipsychotics knock me out and make it very hard to function normally
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're a woman who is pregnant or breast-feeding). If you have abnormally high prolactin levels, it's very common to experience some of the following sexual side effects:
- vaginal dryness
- unwanted hair
- loss of menstrual cycle – but this is unpredictable and your periods may return if your prolactin levels drop back down, so you are still at risk of becoming pregnant if you have unprotected sex
- 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:
- 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.
Antipsychotics can cause various skin problems, such as:
- Allergic rashes. These usually occur within the first two months of starting treatment and disappear when the drug is stopped. If you get a rash, you should go to the doctor straight away to have it checked.
- Increased sensitivity to sunlight, especially at high doses. So if you're taking antipsychotics you may need to take extra care to protect yourself from the sun.
- A blue-grey discoloration in some skin types.
Suicidal feelings or behaviour
You may have felt suicidal before as part of your mental health problem but these feelings may be more likely to occur, or become more intrusive, shortly after starting antipsychotic medication. If you feel suicidal shortly after starting medication, be aware that this may be a side effect of the medication rather than your own true feelings.
Remember: if you feel in immediate crisis you can contact the Samaritans on 116 123 (freephone) or go to your local hospital's A&E department and ask for help.
For more information about suicidal feelings, including information about what kind of support is available, see our pages on how to cope with suicidal feelings and crisis services.
Tardive dyskinesia (TD)
Tardive dyskinesia (TD) is a medical term that describes the involuntary sudden, jerky or slow twisting movements of the face and/or body, caused as an unwanted side effect of medication (mainly antipsychotic drugs). See our pages on tardive dyskinesia for more information about what it is, what treatments and support are available, and how you can cope with the symptoms.
Tardive psychosis is a medical term that descibes new psychotic symptoms which arise after you have been taking antipsychotics for a while, and which are directly caused by the medication (not your original illness returning).
The word 'tardive' means that it's a delayed effect of the medication.
Why does tardive psychosis happen?
Antipsychotic drugs act by blocking receptors for dopamine (a brain chemical) in your brain. But if you take an antipsychotic for a long time, your brain can respond by creating new receptors to replace the ones that the drug is blocking – and your existing receptors may also become extra sensitive. This can mean that you actually end up more likely to have psychotic symptoms as a result of taking the medication. So over time you may find you need to take a higher dose to maintain the antipsychotic effects.
This risk of tardive psychosis is one reason why you'll need to withdraw from your medication very gradually if you decide to come off it – especially if you have been taking it for a long time. Withdrawing slowly gives your brain time to readjust.
Weight gain is a very common side effect of many antipsychotics, in particular the second generation (newer) drugs. It is linked to:
- increased appetite
- decreased activity
- changes in metabolism (the way your body uses food and converts it to energy or stores it as fat)
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 to feel frustrated and upset about noticeable changes in your body.
Awful weight gain, I put on nearly 3st. It made me feel fat and sluggish.
As it may be linked to your metabolism, you may find that dieting doesn't make much difference in controlling your weight gain. But it will certainly help overall if you can:
This information was published in 2016. We will revise it in 2019.