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How cyclobenzaprine (Flexeril) works is not well understood, but it helps alleviate stiffness, pain, and discomfort due to sprains, strains, or injuries to muscles. It is also sometimes prescribed off-label to treat fibromyalgia pain. It is typically only taken one time a day for 2 to 3 weeks. A person should not take cyclobenzaprine for longer than 3 weeks if they have not consulted their healthcare provider.
Cyclobenzaprine may be referred to by the former brand name Flexeril, though generic and other brands exist.
Cyclobenzaprine usually begins working about one hour after it is ingested, relaxing muscles and relieving muscle spasms. Formulations include immediate-release and extended-release. If you are prescribed cyclobenzaprine, follow your healthcare provider’s directions for how to take it.
Cyclobenzaprine works for 4-6 hours. However, the half-life of immediate-release cyclobenzaprine is 18 hours on average, with a range of 8-37 hours. The extended-release form typically has a half-life of 32-33 hours.
Common side effects include:
It is also possible for serious side effects to occur, like seizures, heart arrhythmias, heart attack, or stroke. These are more likely to occur when a person has too much cyclobenzaprine in their system, for instance if their prescription dose is too high or if they are abusing the drug.
Because there is not enough evidence that cyclobenzaprine is effective for long-term use, and because the muscle spasms it is indicated for are generally of short duration, it is not advised to be used for longer than two to three weeks. If cyclobenzaprine is being abused or misused, however, the person may continue to take the medication for much longer and may increase their dose too high, which could lead to dangerous side effects and overdose.
Cyclobenzaprine can increase the effects of CNS depressants, such as alcohol, opioids, allergy medications, and sleeping pills. It can also interact with other medications. If a person is prescribed cyclobenzaprine, they should make sure their health care provider knows all medications they are taking (including over-the-counter medications), as well as if they drink alcohol or use other drugs. This enables the provider to evaluate for any potential interactions and helps them keep the patient safe. Even if it feels like the effects of cyclobenzaprine have worn off, the drug may not be completely eliminated from the body yet and could cause serious interactions with other substances.