Anticholinergics (procyclidine, trihexyphenidyl)

Anticholinergics is the name used to describe a class of Parkinson’s drugs.

You will be prescribed an unbranded anticholinergic medication such as procyclidine or a branded anticholinergic such as Kemadrin.

Due to ongoing issues with fuel supply in the UK, there have been concerns about potential delays in the delivery of drug supplies to pharmacies across all 4 nations. However, the Royal Pharmaceutical Society has made assurances that deliveries of essential medication are continuing as usual to pharmacies. If you're taking medication for your Parkinson's, we recommend waiting until you have used up your existing supply before getting a new one.

If you are having any difficulty with renewing your medication, please get in touch with our helpline, who will be able to advise you further, on 0808 800 0303.

Types of anticholinergic drugs

Below are the types of anticholinergic drugs. The generic names are written in bold and the brand names are written underneath in bullet points. 


  • Kemadrin (tablets, syrup)

  • Kemadrin (solution for injection)

Trihexyphenidyl (benzhexol)

  • Unbranded (tablets, syrup)

Anticholinergics: an introduction

Anticholinergics block a chemical messenger called acetylcholine which is found in your brain and body. It helps to send messages in the brain as well as from your nerves to your muscles. 

In Parkinson’s the effect of acetylcholine is stronger. This can lead to part of the brain becoming overactive and you may experience a tremor. Reducing the effect of acetylcholine can help to treat tremor.

Anticholinergics are not commonly used to treat Parkinson’s. They might help with some Parkinson’s symptoms but can make others worse.

They can be used in younger people with a noticeable tremor. But older people who take anticholinergics are more likely to experience side effects such as confusion  and hallucinations.

If you take them for a number of years, they can be quite difficult to stop and some people experience withdrawal symptoms.

Improving Parkinson’s symptoms

Some anticholinergics may help with tremor with some Parkinson’s symptoms when other medication is no longer working. 

Anticholinergics may help with rigidity, slowness of movement, tremor, speech and writing difficulties, gait, sweating, involuntary movements of the eyes and feeling depressed.

Improving sialorrhoea and drooling

Anticholinergics can reduce the flow of saliva in your mouth which may be helpful if you experience drooling or produce too much saliva (sialorrhoea). However, anticholinergics can also lead to a dry mouth so discuss whether this option is right for you with your health professional.

Limited effect on most Parkinson’s symptoms

Anticholinergics are not a first choice for the treatment of Parkinson’s and may have only a mild effect. 

Memory problems

Anticholinergics are not often given to people with Parkinson’s because they can cause memory problems or make existing problems worse. This can happen at any age, but particularly for older people. 

If you’re taking anticholinergics, your specialist or Parkinson’s nurse must monitor you regularly.

Other side effects

Most of the side effects of anticholinergics are rare, but it is important to know what to look out for. For the full range of side effects, see the patient information leaflet that comes with your anticholinergics medication.

Some of the other possible side effects you may experience with anticholinergics include:

  • mental health issues
  • eye problems
  • constipation 
  • skin reactions
  • trouble urinating

Find out more about the side effects of Parkinson's drugs

Taking anticholinergic drugs: procyclidine and trihexyphenidyl

Procyclidine (Kemadrin) is a type of anticholinergics medication. It may be helpful if you experience muscle spasms (dystonia) which cannot be controlled with other medication. It may also help to control more complex Parkinson’s symptoms such as delusions (seeing, hearing, feeling, smelling or tasting something that isn’t really there).

Taking procyclidine (Kemadrin)

The most recent and complete information on your specific drug will be on your patient information leaflet that comes with your medication packet. Always read it carefully before you start your treatment.

For detailed information you should follow the advice of your healthcare professional about how to take procyclidine (Kemadrin) so that it works well for your Parkinson’s.

You will usually take Kemadrin three times a day. Your specialist or Parkinson’s nurse can increase your dose until it controls your symptoms. 

There is also the option to have procyclidine (Kemadrin) as an injection into your muscles. Alternatively, it is available as a syrup. These options are useful if you have difficulty swallowing tablets. They can also release your medication more quickly.

Procyclidine (Kemadrin) can be taken with levodopa and amantadine medication. Your specialist will be able to discuss whether this option is right for you.

Trihexyphenidyl or benzhexol is a type of anticholinergics medication. It may be helpful if you experience muscle spasms (dystonia), tremor or excessive saliva production (sialorrhoea) which cannot be controlled with other medication. 

Taking trihexyphenidyl medication

You will usually take trihexyphenidyl medication three or four times a day at mealtimes.

If you find that it causes you to experience a dry mouth your specialist may recommend you take trihexyphenidyl before your meal. This can make you feel sick. Instead you can take your medication after you have finished eating. If you do this, you may notice an increased thirst. Water, peppermint or chewing gum can help this issue.

Your specialist will prescribe a small dose of trihexyphenidyl at first and this will be increased until your symptoms are controlled.

You can take trihexyphenidyl with your levodopa medication. Your specialist will be able to discuss whether this option is right for you.

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Drug treatments for Parkinson's (PDF, 756KB)

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Last updated August 2019. We review all our information within 3 years. If you'd like to find out more about how we put our information together, including references and the sources of evidence we use, please contact us at [email protected]