Muscle Relaxants

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Muscle relaxants are used to relieve muscle spasms which may result from some conditions which affect the nervous system. Conditions which may cause muscle spasms include multiple sclerosis, motor neurone disease and cerebral palsy. Muscle spasms and tightness may also follow long-term injuries to the head or back. Muscle spasm can also occur as part of a more short-term condition or injury, such as low back pain or whiplash. Medication helps the muscles to relax, which may also reduce pain and discomfort.

Muscle relaxants are medicines that are used to prevent and reduce muscle spasms and tightness (spasticity). Muscle spasms occur when there is an uncontrolled (involuntary) contraction of a group of muscles. The muscles usually shorten (contract) suddenly; this is often painful. Spasticity occurs when some muscles contract tightly and can then become stiff and harder to use.

Several muscle relaxants are available to prescribe in the UK. They include:

Most muscle relaxant preparations are available as tablets, capsules, or liquids. Baclofen is also available as an injection into the back (an intrathecal injection). Diazepam is also available as a liquid that can be inserted into the back passage (rectum) and there is a diazepam preparation that can be injected into muscle. Cannabis extract is only available as a spray for the mouth. Other treatments sometimes used for muscle spasticity are injections into the affected areas with Botox® (botulinum toxin) and other chemicals.

Muscle relaxants are sometimes used to treat other conditions - for example, diazepam is sometimes used to treat anxiety or difficulty with sleeping (insomnia). It is given as a pre-medication (often called a 'pre-med') before an operation, particularly during procedures that may cause anxiety or discomfort. It can also be used to treat seizures. Rectal diazepam tubes may be prescribed for this, as they are useful if a quick effect is needed or if it is not possible to give the medicine by mouth. The rest of this leaflet only discusses the use of baclofen, dantrolene, diazepam, tizanidine, and cannabis extract when they are used as muscle relaxants.

Some medicines that are given by injection into the vein during surgery are also known as muscle relaxants. They are sometimes called 'neuromuscular blocking drugs' and are used to relax the muscles during surgery. They work in a completely different way to baclofen, dantrolene, diazepam, tizanidine, and cannabis extract and are not discussed here.

Muscle relaxants work by causing the muscles to become less tense or stiff, which in turn reduces pain and discomfort. They do this in different ways. Baclofen, diazepam, methocarbamol and tizanidine act on the central nervous system (brain and spinal cord). Dantrolene works directly on the muscle. Cannabis extract works on the brain and spinal cord as well as the muscles. Because dantrolene only works on the muscles it is thought to have fewer side-effects compared with other muscle relaxants. For this reason, dantrolene is often the first muscle relaxant to be prescribed for people with long-term muscle spasms.

Muscle relaxants are used to relieve muscle spasms which may result from some conditions which affect the nervous system, such as:

  • Multiple sclerosis.
  • Motor neurone disease.
  • Cerebral palsy.
  • Long-term injuries to the head or back.

Cannabis extract is usually started by a consultant in a hospital. It is normally prescribed for people with multiple sclerosis who have tried other muscle relaxants which are not working. In most cases it is given as a four-week trial to see if it helps with symptoms.

In addition, diazepam may be used to relieve lower back pain, or neck pain in conditions such as whiplash. It is addictive so cannot be used for more than a week or two. Methocarbamol is also used for muscle spasm in people with low back pain. Much of the pain in these conditions is due to muscle spasm. The cause of the spasm is different to the nervous system conditions above.

See separate leaflets called Multiple Sclerosis, Motor Neurone DiseaseCerebral Palsy and Nonspecific Lower Back Pain in Adults for more details.

These medicines are usually taken by mouth (tablets, capsules or liquids). In general, your doctor will start off with a low dose and increase this gradually over a number of weeks. This is in order to help your body get used to these medicines. Injections into the back are always started in the hospital.

Cannabis extract is a spray for the mouth. It should be sprayed under the tongue or on to the inside of the cheek once or twice a day. Always change the area in your mouth where you spray, to prevent irritation of the mouth. Like other muscle relaxants you will normally start off with a low dose. The number of sprays used is normally increased over a number of days.

As with most medicines, muscle relaxants have a number of possible side-effects. However, not everyone experiences them and they usually improve as your body adjusts to the new medicine. Most muscle relaxants cause muscle weakness as a side-effect. It is not possible in this leaflet to list all the possible side-effects for these medicines. However, see below for a list of the most common side-effects. For more detailed information, see the leaflet that comes with the medicine packet.

  • Baclofen - feeling sick, tiredness, drowsiness, problems with eyesight, weakness, dizziness, light-headedness, headache, dry mouth, breathing difficulties, aching muscles, sleeplessness or nightmares, feeling anxious or agitated, confusion, unsteadiness, increased need to pass urine, shakiness, increased sweating, and skin rash.
  • Dantrolene - feeling dizzy, sleepy, tired, or generally unwell, diarrhoea, feeling or being sick, tummy (abdominal) pain, headache, loss of appetite, rash, speech or sight difficulties, high temperature (fever), chills, difficulty in breathing, seizures. It may also cause inflammation of the lining around the heart (sometimes with fluid in the lungs). Liver toxicity is also a possible side-effect of dantrolene.
  • Diazepam - feeling sleepy, weak, or light-headed, forgetfulness, feeling confused or unsteady, feeling (or being) aggressive.
  • Tizanidine - feeling drowsy, dizzy, or tired, dry mouth, feeling sick, upset stomach, feeling light-headed, especially when you stand up. Other less common side-effects include difficulty sleeping, hallucinations, and a slower heart rate.
  • Methocarbamol - forgetfulness, allergic reactions, being anxious, blurred vision, a slow heart rate, being confused or dizzy, headache, heartburn, feeling or being sick, itching, rash, and low blood pressure.
  • Cannabis extract - feeling dizzy, depressed mood, diarrhoea or constipation, mouth ulcers or pain, feeling tired or sick, appetite changes. Hallucinations have also been reported.

For a full list of people who should not take each type of muscle relaxant, refer to the specific leaflet for that medication.

  • Baclofen should not usually be given to people who have a stomach ulcer, epilepsy, mental health problems or diabetes.
  • Dantrolene should not be given to people with liver, heart or breathing problems.
  • Diazepam should be avoided in people who have severe breathing difficulties - for example, people who have myasthenia gravis and people with lung problems.
  • Tizanidine should not usually be given to elderly people, or people who have severe problems with their liver.
  • Methocarbamol should not be used for people who have myasthenia gravis or severe breathing problems. It also should not be used in people with epilepsy or brain damage.
  • Cannabis extract can only be prescribed by specialists for people with multiple sclerosis. People who have a personal or family history of hallucinations or delusions or any other severe psychiatric disorder should not take cannabis extract.

There are a number of other things to consider when taking muscle relaxants:

  • These medicines can cause drowsiness. Do not drive or operate machinery if you feel drowsy when taking these medicines and avoid drinking alcohol.
  • Baclofen should not be stopped suddenly. The dose should be lowered slowly over a few weeks and then stopped.
  • Diazepam - people who take this medicine continuously for more than two weeks can become dependent on it. This means that withdrawal symptoms occur if the tablets are stopped suddenly. See separate leaflet called Benzodiazepines and Z drugs for more details.

No, you cannot buy muscle relaxants. They are only available from your pharmacy on prescription.

If you think you have had a side-effect to one of your medicines, you can report this on the Yellow Card Scheme. You can do this online at the following web address: www.mhra.gov.uk/yellowcard.

The Yellow Card Scheme is used to make pharmacists, doctors and nurses aware of any new side-effects that your medicines or any other healthcare products may have caused. If you wish to report a side-effect, you will need to provide basic information about:

  • The side-effect.
  • The name of the medicine which you think caused it.
  • The person who had the side-effect.
  • Your contact details as the reporter of the side-effect.

It is helpful if you have your medication and/or the leaflet that came with it with you while you fill out the report.

Original Author:
Jenny Whitehall
Current Version:
Peer Reviewer:
Dr John Cox
Document ID:
28428 (v2)
Last Checked:
18/12/2015
Next Review:
17/12/2018
The Information Standard - certified member
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