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Muscle relaxants

Muscle relaxants are medicines that help the muscles to relax, which may also reduce pain and discomfort.

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.

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What are muscle relaxants?

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.

What muscle relaxants are available?

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.

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Can I buy muscle relaxants?

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

When are muscle relaxants prescribed?

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

Cannabis extract is always started by a consultant in a hospital and is only available in the UK for a very limited range of uses. The muscle relaxant indication is 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, and can be continued if the symptoms have improved by at least 20%, using a numerical rating scale.

In addition, diazepam is occasionally used to relieve lower back pain, or neck pain in conditions such as whiplash. It is addictive so is not usually used for more than a few days, and it is used less often than in the past, because we know that it doesn't have a very strong effect; in fact, the National Institute for Health and Care Excellence (NICE) say that its effect is sometimes worse than that of a placebo tablet. 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 in back pain is different to in the nervous system conditions above, such as multiple sclerosis.

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How should muscle relaxants be taken?

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.

Muscle relaxant side-effects

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.

  • 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.

Who cannot take muscle relaxants?

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, Parkinson's disease, a history of substance abuse or diabetes, and caution should be advised before prescribing for people who are very elderly.

  • Dantrolene should not be given to people with liver, heart or breathing problems, or reduced lung function.

  • 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, 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, and caution should be used if considering it for people who have epilepsy or significant cardiovascular disease.

Other considerations

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.

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.

Things to consider when taking muscle relaxants

  • These medicines can cause drowsiness. If you feel drowsy when taking these medicines, do not operate machinery, do not drive, and do not drink 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 too long can become dependent on it. This means that withdrawal symptoms occur if the tablets are stopped suddenly. See the separate leaflet called Benzodiazepines and Z Drugs for more details.

How do muscle relaxants work?

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.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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