Cyclobenzaprine for acute muscle pain (Amrix, Flexeril)

Cyclobenzaprine is used to relive short-term muscle pain caused by 'overstretching' injuries. You should not need to take this medicine for more than two to three weeks.

This medicine is used in addition to rest and physiotherapy to relieve pain while you recover from the muscle injury.

Taking cyclobenzaprine may make you feel sleepy or dizzy. If this happens do not drive and do not use tools or machines.

Try not to drink any alcohol while taking cyclobenzaprine as this will increase the chance of you feeling sleepy.

Type of medicineSkeletal muscle relaxant
Used forRelieving acute muscle pain caused by injuries such as strains and sprains
Also calledAmrix®; Flexeril®
Available asTablets, extended-release capsules

A short-term (acute) injury to the muscles, or the tissues which connect them, is usually the result of overstretching during sport or physical exercise. The most common injuries are strains and sprains which result in pain, swelling and restricted movement.

A strain refers to a painful condition brought about by inflammation, overuse (or using in an unbalanced way), and overstretching or tearing of muscles, tendons or joints.

A sprain is an injury to the band (ligament) which connects two or more bones to a joint. A sprain is usually caused by the joint being forced suddenly outside its usual range of movement. 

Cyclobenzaprine (not available in the UK and Europe) helps relieve the pain of muscle spasms caused by these types of injury. It works by relaxing the muscles, which reduces pain and discomfort and makes movement easier. Cyclobenzaprine is used in addition to rest and physiotherapy to help you recover from the injury.

Some medicines are not suitable for people with certain conditions, and sometimes a medicine may only be used if extra care is taken. For these reasons, before you start taking cyclobenzaprine it is important that your physician or pharmacist knows:

  • If you are pregnant, trying for a baby, or breast-feeding.
  • If you have had a heart attack or you have any other heart problems.
  • If you have epilepsy or have ever had a fit (seizure).
  • If you have liver or kidney problems.
  • If you have an overactive thyroid gland (hyperthyroidism).
  • If you have a condition which makes it difficult for you to pass urine (urinary retention).
  • If you have raised pressure in your eye (glaucoma).
  • If you are taking, or have recently stopped taking, a type of antidepressant medicine known as a monoamine-oxidase inhibitor (MAOI).
  • If you are taking or using any other medicines. This includes any medicines you are taking which are available to buy without a prescription as well as herbal and complementary medicines.
  • If you have ever had an allergic reaction to a medicine.
  • Before you start this treatment, read the manufacturer's printed information leaflet from inside your pack. The leaflet will give you more information about cyclobenzaprine and a full list of side-effects which you may experience from taking it.
  • Take cyclobenzaprine exactly as your physician tells you to. Your dose will be on the label of the pack to remind you. The tablets are available in three different strengths: 5 mg, 7.5 mg and 10 mg. The usual dose is one 5 mg tablet taken three times daily. Extended-release capsules are available in two strengths: 15 mg and 30 mg. The usual dose is one 15 mg capsule taken once daily with food.
  • Your physician may decide to increase your dose depending on how well you respond to the medicine. 
  • Swallow the tablets whole with a glass of water. Amrix® extended release capsules should be swallowed whole or can be opened and the contents sprinkled on to a spoonful of apple sauce. This should then be swallowed immediately without chewing. Rinse the mouth with water afterwards and safely dispose of the empty capsule.
  • Try to take your doses at the same times of day each day, as this will help you to remember to take them. If you do forget to take a dose, take it as soon as you remember unless it is nearly time for your next dose, in which case leave out the missed dose. Do not take two doses together to make up for a forgotten dose.
  • Following a sprain or strain the usual advice is to pay the PRICE (Protection, Rest, Ice, Compression, and Elevation) and avoid HARM (Heat, Alcohol, Running, and Massage) for the first 48-72 hours after injury.
  • You should not play sport or do any vigorous exercise involving the damaged part while you are taking cyclobenzaprine.
  • Try to keep any appointments with your physician or physiotherapist. This is so they can check on your progress.
  • Cyclobenzaprine may cause drowsiness. It may also increase the time it takes for you to react, so it can impair your judgement. If this happens do not drive and do not use tools or machines. 
  • It is recommended that you do not drink alcohol while you are taking cyclobenzaprine. This is because it increases the chance that you will experience side-effects such as feeling sleepy or dizzy.
  • With proper rest and care most sprains and strains heal within a few weeks. You should not need to continue taking cyclobenzaprine for longer than three weeks. If your injury is still causing pain after this time, make an appointment to see your physician or speak to a pharmacist.
  • If you are having an operation or dental treatment, tell the person carrying out the treatment which medicines you are taking.
  • If you buy any medicines, check with a pharmacist that they are safe to take with your other medicines.

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the most common ones associated with cyclobenzaprine. You will find a full list in the manufacturer's information leaflet supplied with your medicine. The unwanted effects often improve as your body adjusts to the new medicine, but speak with your physician or pharmacist if any of the following continue or become troublesome.

Common cyclobenzaprine side-effectsWhat can I do if I experience this?
Feeling sleepy, tired or dizzyIf this happens, do not drive and do not use tools or machines
Tummy (abdominal) pain, feeling or being sick, diarrheaDrink plenty of water and stick to simple foods - avoid rich or spicy meals
HeadacheAsk your pharmacist to recommend a suitable painkiller
Dry mouthTry chewing sugar-free gum or sugar-free candy

Sleeping difficulties, mood changes, confusion, fast heartbeat, needing to pass urine more often or difficulty passing urine, feeling shaky, increased sweating, and rash

If any of these become troublesome, discuss them with your physician

Cyclobenzaprine can affect the levels of a chemical called serotonin in the brain. On rare occasions, medicines that raise the level of serotonin can cause it to go too high and cause problems. The risk is higher if you are taking more than one medicine with this effect. Other examples include selective serotonin reuptake inhibitor (SSRI) antidepressant medicines and opioid painkillers such as tramadol and morphine. Seek medical attention if you develop a combination of the following:

  • Stiff muscles or 'jerky' movements.
  • Unusually fast heartbeat.
  • High temperature (fever), feeling or being sick, diarrhea.
  • Feeling delirious or seeing visions (hallucinating).

If you experience any other symptoms which you think may be due to this medicine, speak with your physician or pharmacist.

  • Keep all medicines out of the reach and sight of children.
  • Store in a cool, dry place, away from direct heat and light.

Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine, go to the emergency room of your local hospital. Take the container with you, even if it is empty.

This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.

Do not keep out-of-date or unwanted medicines. Ask your pharmacist about ways to dispose of medicines safely in your local area.

If you have any questions about this medicine ask your pharmacist.

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Author:
Mr Michael Stewart
Peer Reviewer:
Dr Hayley Willacy
Document ID:
29314 (v1)
Last Checked:
01 March 2017
Next Review:
29 February 2020

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. Patient Platform Limited has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.