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Antipsychotics

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

What dosage of antipsychotics should I be on?

Your dosage means how much of your antipsychotic medication you should take (your dose), and how often you should take it.

Finding the best dosage for you will depend on a lot of factors. These include:

  • The specific drug you've been prescribed. Safe dosages for different antipsychotics can vary widely.
  • Whether you're taking other medication. Some drugs can interact with antipsychotics if you take them at or around the same time.
  • What you find works for you. Medication work differently for everyone. Its effects may depend on factors like your age, weight, genes, general health, liver and kidney function, and whether you're able to take the drug as recommended.

You and your doctor or psychiatrist can work together to see whether your antipsychotic helps you and how well it suits you. They should be able to tell you how the drug may help you, and when you are likely to feel the drug’s effects. The aim should be to find a dosage where the benefits outweigh any negative side effects.

Remember: you have a right to know what dosage you have been prescribed, and why.

How can I work out my best dosage?

  • You should always start at a low dose. For many people, low maintenance doses are as effective as higher doses. The dose should still be enough for the medication to have an effect.
  • You should try taking the dosage you've been prescribed for four to six weeks to see how it's working.
  • Your doctor or psychiatrist may then adjust your dose gradually. But they should only do this if you both agree it is necessary.
  • You may find that your medication isn't working, even if your dose is increased to the recommended limit. Or you may find that your medication is causing unpleasant side effects that are difficult to live with. In this case, your doctor or psychiatrist should consider offering you a different antipsychotic drug.
  • Your doctor or psychiatrist should clearly record any decisions about your medication in your medical notes. This includes whether to start, continue, stop or change to another drug. It is especially important if your doctor or psychiatrist prescribes a dose that's outside the usual recommended range for that drug.

What are the effects of taking a higher dose?

The higher your dose, the more likely you are to experience problems with side effects. For example, certain antipsychotics may cause side effects which affect your ability to:

  • get up in the morning
  • move your muscles naturally
  • take part in everyday activities.

Moderate to high doses of antipsychotics may also increase the risk of tardive dyskinesia. This is a serious side effect which causes movements in your face or body that you can’t control.

PRN prescribing

PRN prescribing means giving you extra doses of your medication, in addition to your regular daily dose. 'PRN' stands for 'pro re nata', which means ‘as the circumstances require’ in Latin. So it only happens in certain circumstances.

You are most likely to be given a PRN dose if you are staying in hospital, either because:

  • the medical staff think you need a bit more medication in some situations, or
  • you've asked for a bit more medication in some situations.

Any PRN doses should be carefully recorded in your medical notes. Your doctor or psychiatrist should also monitor you to make sure that you don’t receive a daily dose that's too high.

Is my daily dose too high?

The British National Formulary (BNF) recommends maximum doses for many medications licensed in the UK, including antipsychotics. You can search the BNF’s A to Z list of drugs to find information about any medication you’ve been prescribed, including details of recommended doses.

In most cases, antipsychotics aren’t licensed for use above the maximum recommended dose published by the BNF. But there are some situations where you may end up with a total daily dose above the recommended maximum. These include:

  • If your doctor or psychiatrist prescribes you a higher dose than recommended daily dose. They can choose to do this at their discretion, but it should not be common.
  • If you are taking more than one antipsychotic at the same time.
  • If you are in hospital receiving a PRN prescription. This is the most likely situation in which your daily dose may end up higher than the recommended limit.

You have a right to know how much medication you’re taking in total, including PRN doses. If you aren’t confident about working this out, your doctor, psychiatrist or pharmacist should be able to explain it to you.

Your pharmacist may also have a specific chart published by the Prescribing Observatory for Mental Health UK (POMH-UK) to work out antipsychotic dosages. They can use this as a guide to help you work out your overall dosage more easily.

If you are prescribed more than the recommended daily limit, your doctor or psychiatrist has a duty to review this every day. But you can always speak to your doctor or psychiatrist if you feel your daily dose is too high. You can ask them to review your dosage at any time, even if it is within the recommended range.

See our pages on coming off antipsychotics and alternatives to antipsychotics for information about other options.

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

References and bibliography available on request.

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