Cyclobenzaprine is a prescription muscle relaxant, and it is structurally related to tricyclic antidepressants. It is commonly referred to by the brand name Flexeril, though other brands and generics are available.

How cyclobenzaprine 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, but it is recommended that cyclobenzaprine should not be taken for more than 2 to 3 weeks.

Cyclobenzaprine usually begins working about one hour after it is ingested, relaxing muscles and relieving muscle spasms. Flexeril should not be taken more than three times a day. A common starting dose for adults is 5 mg three times per day. Doses should not exceed 60 mg per day.

Cyclobenzaprine’s Effectiveness Timeframe

cyclobenzaprine effectiveness

Cyclobenzaprine actively works on painful muscles 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.

The most common side effect from cyclobenzaprine is drowsiness, which could last after the muscle-relaxing effects have ended. Many people who take this medication report feeling fatigued or sleepy.

Common Side Effects

Common side effects include:

  • Drowsiness
  • Blurred vision
  • Dry mouth
  • Lightheadedness
  • Dizziness

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 should not be used for more 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 beyond the recommended maximum, 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.

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