Trihexyphenidyl hydrochloride for dystonia

This leaflet is for parents and carers about how to use this medicine in children. Our information may differ from that provided by the manufacturers, because their information usually relates to adults. Read this leaflet carefully. Keep it somewhere safe so that you can read it again.

Name of medicine

Trihexyphenidyl hydrochloride (also known as benzhexol hydrochloride)

Brand name: Broflex®

This leaflet is about the use of trihexyphenidyl hydrochloride for the treatment of dystonic muscle spasms (also called dystonia).

Why is it important for my child to take trihexyphenidyl hydrochloride?

In children with dystonic muscle spasms (also called dystonia), the muscles have contracted too much and are too tight so that the head, arms or legs are held in awkward or uncomfortable positions. Trihexyphenidyl hydrochloride blocks the effects of a chemical messenger called acetylcholine that is released from the nerves to make the muscle contract. It also helps the muscles to relax. This should allow a better range of movement in the affected part of the body and reduce painful spasms.

What is trihexyphenidyl hydrochloride available as?

Tablets: 2 mg, 5 mg

Liquid medicine: 5 mg in 5 mL (pink syrup) 

When should I give trihexyphenidyl hydrochloride

Trihexyphenidyl hydrochloride may be given once, twice or three times a day, depending on the age and weight of the child and their condition. Your doctor will discuss this with you, and when best to give the medicine to treat your child’s most difficult spasms.

Once a day: this can be at a time of day that works best for your child.

Twice a day: this should be once in the morning and once in the evening. Ideally, these times are 10–12 hours apart, for example some time between 7 and 8 am, and between 7 and 8 pm.

Three times a day: this should be once in the morning, once in the early afternoon and once in the evening. Ideally, these times are at least 6 hours apart.

Give the medicine at about the same time(s) each day so that this becomes part of your child’s daily routine, which will help you to remember.

How much should I give?

Your doctor will work out the amount of trihexyphenidyl hydrochloride that is right for your child. The dose will be shown on the medicine label.

You will probably start with a low dose and then gradually increase it, depending on how well it works and whether it causes any side-effects. Your doctor will explain what to do. Do not change the dose without talking to your doctor first. 

It is important that you follow your doctor’s instructions about how much to give.

How should I give trihexyphenidyl hydrochloride?


Tablets should be swallowed with a glass of water, milk or juice. Your child should not chew the tablets. You can crush the tablet and mix it with a small amount of soft food such as yogurt, honey or jam. Make sure your child swallows it all straight away.

Liquid medicine

Measure out the right amount using a medicine spoon or oral syringe. You can get these from your pharmacist. Do not use a kitchen teaspoon as it will not give the right amount.

When should the medicine start working?

The medicine starts to work straight away. However, because the dose is usually increased gradually, it may take some weeks before you see the full effect. Your doctor will discuss treatment goals with you before starting treatment with trihexyphenidyl hydrochloride.

What if my child is sick (vomits)?

If your child is sick less than 30 minutes after having a dose of trihexyphenidyl hydrochloride, give them the same dose again.

If your child is sick more than 30 minutes after having a dose of trihexyphenidyl hydrochloride, you do not need to give them another dose. Wait until the next normal dose.

What if I forget to give it?

If you usually give it once a day: Give the missed dose when you remember, as long as this is at least 12 hours before the next dose is due. You do not need to wake up a sleeping child to give a missed dose.

If you usually give it twice a day: If you remember up to 4 hours after you should have given a dose, give your child the missed dose. For example, if you usually give a dose at about 7 am, you can give the missed dose at any time up to 11 am. If you remember after that time, do not give the missed dose. Just give the next dose as usual.

If you usually give it three times a day: Do not give the missed dose. Just give the next dose as usual.

Never give a double dose of trihexyphenidyl hydrochloride.

What if I give too much?

If you think you may have given your child too much trihexyphenidyl hydrochloride, contact your doctor or local NHS services (111 in England and Scotland; 111 or 0845 4647 in parts of Wales) or take your child to hospital. Take the medicine container or packet with you, even if it is empty. This will be useful to the doctor. Have the packet with you if you telephone for advice.

It can be dangerous to give too much trihexyphenidyl hydrochloride.

Are there any possible side effects?

We use medicines to make our children better, but sometimes they have other effects that we don’t want (side effects).

Side effects you must do something about

If your child cannot urinate (do a wee) when they feel they need to, take them to your doctor or to hospital straight away.

Your child’s eyesight may become blurred (fuzzy). If this happens, contact your doctor for advice.

Other side-effects you need to know about

If any of these side-effects become a problem, discuss this with your doctor. They may suggest a lower dose for a short time to help your child’s body get used to the medicine. Do not change the dose without discussing this with your doctor first.

  • Your child may have a dry mouth. Eating citrus fruits (e.g. oranges) and sipping water may help.

  • Your child may get constipation (difficulty doing a poo), and feel sick or be sick (vomit).

  • They may seem agitated, show changes in mood, have difficulty remembering things, may seem confused and may have hallucinations (seeing things that are not there).

Can other medicines be given at the same time as trihexyphenidyl hydrochloride?

  • You can give your child medicines that contain paracetamol or ibuprofen, unless your doctor has told you not to.

trihexyphenidyl hydrochloride should not be taken with some medicines that you get on prescription. It is important to tell your doctor and pharmacist about any other medicines your child is taking before starting trihexyphenidyl hydrochloride.

Check with your doctor or pharmacist before giving any other medicines to your child. This includes herbal and complementary medicines.

Is there anything else I need to know about this medicine?

Trihexyphenidyl hydrochloride is a useful medicine for children with dystonia. It may take a while for your child to get used to this medicine. It can take some time to find the dose that provides the most benefit without too many side-effects. Sometimes the dose may be reduced for a short while because of side-effects but it may then be possible to increase it again to get more benefit.

It is important that you follow your doctor’s instructions about how much to give. Discuss any concerns you have with your doctor.

General advice about medicines

  • Try to give medicines at about the same times each day, to help you remember.
  • If you are not sure a medicine is working, contact your doctor but continue to give the medicine as usual in the meantime. Do not give extra doses, as you may do harm.
  • Only give this medicine to your child. Never give it to anyone else, even if their condition appears to be the same, as this could do harm.
  • Make sure that you always have enough medicine. Order a new prescription at least 2 weeks before you will run out.
  • Make sure that the medicines you have at home have not reached the ‘best before’ or ‘use by’ date on the packaging. Give old medicines to your pharmacist to dispose of.

If you think someone else may have taken the medicine by accident, contact your doctor straight away.

Where should I keep this medicine?

  • Keep the medicine in a cupboard, away from heat and direct sunlight.
  • It does not need to be kept in the fridge.
  • Make sure that children cannot see or reach the medicine.
  • Keep the medicine in the container it came in.

Who to contact for more information?

Your doctor, pharmacist or nurse will be able to give you more information about trihexyphenidyl hydrochloride and about other medicines used to treat dystonia.

England: NHS 111

Tel 111

Scotland: NHS 24

Northern Ireland: NI Direct

Wales: NHS 111 Wales

Dystonia UK

Copyright disclaimer

Version [1]. © NPPG, RCPCH and WellChild, all rights reserved. Review by September 2013.

The primary source for the information in this leaflet is the British National Formulary for Children. For details on any other sources used for this leaflet, please contact us through our website,

We take great care to make sure that the information in this leaflet is correct and up-to-date. However, medicines can be used in different ways for different patients. It is important that you ask the advice of your doctor or pharmacist if you are not sure about something. This leaflet is about the use of these medicines in the UK, and may not apply to other countries. The Royal College of Paediatrics and Child Health (RCPCH), the Neonatal and Paediatric Pharmacists Group (NPPG), WellChild and the contributors and editors cannot be held responsible for the accuracy of information, omissions of information, or any actions that may be taken as a consequence of reading this leaflet.