Flexeril is a prescription medicine used to treat the symptoms of muscle spasms. Flexeril may be used alone or with other medications. Flexeril belongs to a class of drugs called Skeletal Muscle Relaxants. It is not known if Flexeril is safe and effective in children younger than 15 years of age.
Half-life: 18 hours (range: 8-37 hours; n=18)
What is the half-life of Flexeril?
The FDA reports cyclobenzaprine’s half-life to be 18 hours with a range of 8-37 hours. For elderly people, however, Flexeril has a mean half-life of 33.4 hours and 46.2 hours for people with hepatic insufficiency.
The FDA also reports the drug “accumulates when dosed three times a day, reaching steady-state within 3-4 days at plasma concentrations about four-fold higher than after a single dose.”
How long does Flexeril stay in your system?
Flexeril is likely detectable in your system for the following time frames:
- Urine: Roughly 3 to 8 after last use
- Saliva: Roughly 36 hours after last use
- Plasma: The FDA states that “plasma clearance is 0.7 L/min”
- Hair: N/A
(Numbers above are merely estimates, and may vary based on several factors, such as age and other medical conditions.)
How long does it take for a muscle relaxer to wear off?
The amount of time it takes for Flexeril to wear off may depend on the dosage you are taking, as well as your individual health profile. Some studies show that the duration of action can be from 12 hours to 24 hours.
In some cases, doctors recommend their patients to take Flexeril three times per day to prevent the medicine from “wearing off.” If you have concerns about the effectiveness of Flexeril on your specific symptoms, talk with your doctor about the best dosage for you.
How long does Flexeril take to work?
In most cases, Flexeril works within hours of taking a dose, but time may vary depending on the individual and their dosage amount.
What are the possible side effects of Flexeril?
Flexeril may cause serious side effects including:
- fast or irregular heartbeat,
- chest pain or pressure,
- pain spreading to your jaw or shoulder,
- sudden numbness or weakness (especially on one side of the body),
- slurred speech, and
- balance problems
Get medical help right away, if you have any of the symptoms listed above.
The most common side effects of Flexeril include:
- dry mouth,
- upset stomach,
- nausea, and
Tell the doctor if you have any side effect that bothers you or that does not go away.
These are not all the possible side effects of Flexeril. For more information, ask your doctor or pharmacist.
Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
What happens if I miss a dose?
Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.
What happens if I overdose?
Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of cyclobenzaprine can be fatal. Overdose symptoms may include severe drowsiness, vomiting, fast heartbeats, tremors, agitation, or hallucinations.
What to avoid
Avoid driving or hazardous activity until you know how cyclobenzaprine will affect you. Your reactions could be impaired. Avoid drinking alcohol. Dangerous side effects could occur.