Finding the best daily dose of antipsychotic for you will depend on lots of factors, such as:
- The specific drug you've been prescribed. Safe dosage rates for different antipsychotics can vary widely – you can look up the recommended range for each drug in our antipsychotics A-Z.
- If you're taking other medication because some drugs can interact with antipsychotics.
- What you find works for you. Drugs work differently for everyone – they can be influenced by all sorts of personal factors such as 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 should think of a new antipsychotic as a trial, to see whether it helps you and how well it suits you. The aim should be to find a daily dose where the benefits outweigh any side effects, so you can lead the life you want as far as possible.
Key facts about antipsychotic dosage
As a guideline:
- You should always start at a low dose. For many people, low maintenance doses are as effective as higher doses.
- You should try the dose you've been prescribed for four to six weeks to see how it's working.
- Your doctor may then increase it gradually, but only if you both agree it's necessary.
- If you find that your medication isn't working, even after your dose has been increased, then your doctor should consider offering you a different drug rather than continuing to increase the dose of the one you started with.
Be aware:
- The higher your dose, the more likely you are to experience problems with side effects. For example:
- high doses of first generation antipsychotics in particular are more likely to cause side effects which make it really hard for you to get up in the morning, move your muscles naturally and take part in everyday activities.
- moderate to high doses of antipsychotics increase the risk of tardive dyskinesia (a serious side effect)
- You have a right to know what dosage you have been prescribed, and why.
- The reasons for any decisions made about your medication – including whether to start, continue, stop or change to another drug – should be clearly recorded by your doctor in your medical notes. This is especially important if your doctor prescribes a dose that's outside the usual recommended range for the drug.
Prn prescribing
Prn prescribing means that you may occasionally be given 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.
This is most likely to happen if you are an in-patient 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
If you're given prn doses of medication, this should be very carefully recorded in your notes and monitored by your doctor to make sure that you do not accidentally end up receiving a daily dose that's too high.
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Is my daily dose too high?
Generally, antipsychotics aren’t licensed for use above the maximum dosages published in the BNF (British National Formulary – the main drug reference book for prescribers). The BNF gives maximum dosages for some antipsychotics but not all of them. You can find these details for each drug in our antipsychotics A-Z.
However, there are some circumstances where you may end up with a total daily dose above the recommended maximum. These include:
- If your doctor prescribes you a higher than recommended daily dose. They can choose to do this at their discretion, but it's not common.
- If you are taking more than one antipsychotic at the same time.
- If you are an in-patient receiving prn medication. This is the most likely scenario in which your daily dose may end up higher than the recommended maximum.
You have a right to know how much medication you're taking in total, including prn doses – so if you're not confident in working this out for yourself, your doctor or pharmacist should be able to explain it to you. Ask them to help you calculate your dose of each drug as a percentage of the BNF recommended maximum for that drug, then add the percentages together to see if the total comes to more than 100%. More than 100% in total would mean your daily dose is exceeding the recommended maximum. Your pharmacist may be able to access a antipsychotic dosage ready reckoner chart published by the Prescribing Observatory for Mental Health UK (POMH-UK) as a guide to help you work out the percentages more easily.
If you are being prescribed more than the recommended daily maximum, your doctor has a duty to review this every day. But even if your dosage is within the recommended range, if you feel that your daily dose is too high for you then it's important to discuss it with your doctor and ask them to review it.
See our pages on coming off antipsychotics and alternatives to antipsychotics for information about other options.
This information was published in 2016. We will revise it in 2019.
