Trihexyphenidyl hydrochloride for dystonia

node leader
Share this page: 

Trihexyphenidyl hydrochloride for dystonia

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

This Information Standard quality markleaflet has been written specifically for parents and carers about the use of this medicine in children. The information may differ from that provided by the manufacturer. Please read this leaflet carefully. Keep it somewhere safe so that you can read it again. 

Name of drug

Trihexyphenidyl hydrochloride (also known as benzhexol hydrochloride)
Brand name: Broflex®

Why is it important for my child to take this medicine?

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. Trihexylphenidyl 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 it?

Tablets should be swallowed with a glass of water, milk or juice. Your child should not chew the tablet.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 straight away, without chewing

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?

It may be dangerous to give too much trihexyphenidyl hydrochloride. If you think you may have given your child too much, contact your doctor or NHS Direct (0845 4647 in England and Wales; 08454 24 24 24 in Scotlanc) or take your child to hospital. 

Take the medicine container or packaging with you, even if it is empty. This will be useful to the doctor. Have the medicine or packaging with you if you telephone for advice.

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 has any difficulty with urination (doing a wee), contact your doctor straight away. If your child cannot urinate when they feel they need to, take them to your doctor or to hospital straight away, as there is a risk of damage to the kidneys. 

  • Your child’s eyesight may become blurred (fuzzy). If this happens, contact your doctor for advice.
Other side-effects you need to know about 
  • Your child may get constipation (difficulty doing a poo), and feel sick or be sick (vomit). 
  • They may have a dry mouth. Taking sips of water or sucking on citrus fruits (e.g. oranges) may help.
  • 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). 
  • 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.

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. Tell your doctor and pharmacist about any other medicines your child is taking before giving trihexyphenidyl hydrochloride. 
  • Check with your doctor or pharmacist before giving any other medicines to your child. This includes herbal or complementary medicines.

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

  • Trihexylphenidyl 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. 

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

  • 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 medicine you have at home has not reached the ‘best before’ or ‘use by’ date on the packaging. Give old medicines to your pharmacist to dispose of.

Where I should keep this medicine?

  • Keep the medicines 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.

You can also get useful information from: 
Publication date: