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Drug Info

How long does cyclobenzaprine last?

This muscle relaxant is typically effective for four to six hours
Heidi Borst
By | Jul. 24, 2024 Medically reviewed by Madeline Remelius, Pharm.D., BCPS

Key takeaways

  • Cyclobenzaprine starts working one to two hours after taking it and typically remains effective for four to six hours.

  • Factors such as metabolism, dosage, and concomitant medication use can influence the drug’s duration of action.

  • Cyclobenzaprine may cause drowsiness that lingers the following day. Other common side effects include constipation, dry mouth, and dizziness.

Cyclobenzaprine hydrochloride (brand names Flexeril and Amrix) is a widely used skeletal muscle relaxant that is FDA approved to be used alongside rest and physical therapy for relief of muscle spasms associated with acute, painful musculoskeletal conditions. It provides short-term relief from acute muscle spasms and may help increase the range of motion. It is also prescribed off-label to treat pain from fibromyalgia, temporomandibular joint (TMJ) disorders, and as an adjunct treatment for opiate withdrawal symptoms.

Cyclobenzaprine acts on the brain and central nervous system (CNS) to inhibit chemical signals that trigger muscle contractions. In other words, it allows the muscles to relax. 

Cyclobenzaprine typically remains effective for four to six hours. Still, factors like metabolism, dosage, and the presence of other medications or substances in the body can impact how long it takes to wear off.

How long does cyclobenzaprine last?

“Cyclobenzaprine is often used alongside rest and physical therapy to help speed up recovery from muscle-related pain,” says Taher Saifullah, MD, a pain management specialist and founder of Spine and Pain Institute Los Angeles. It is available in immediate-release tablets and extended-release (ER) capsules.

  • Immediate-release: This formulation lasts for four to six hours, with an average half-life of 18 hours. Dosage ranges from 5 to 10 mg, three times daily.
  • Extended-release: This form works for up to 24 hours, with an average half-life of 32 hours. The dosage is 15 to 30 mg, taken once daily.

“Cyclobenzaprine typically peaks in your system between three and eight hours after you take it,” notes Dr. Saifullah. He says it is not uncommon for the prescription drug to induce drowsiness, which may persist into the following day—particularly when higher doses are taken or when the drug is used for an extended period.

According to Dr. Saifullah, the following factors can impact the duration of action:

  • Age: Older adults might experience longer-lasting effects because their bodies metabolize the drug more slowly.
  • Liver function: Those with liver issues might have a prolonged duration of action due to slower drug breakdown.
  • Medications: Some medications can interfere with the enzymes that metabolize cyclobenzaprine, affecting how long it stays active.
  • Body composition: Cyclobenzaprine is stored in fat tissue, so individuals with higher body fat may notice longer-lasting effects.

Cyclobenzaprine, similar in chemical structure to tricyclic antidepressants (TCAs), is metabolized primarily through the liver and excreted through the urine, says Wendi D Jones, Pharm.D., a pharmacist with AspenRx Health. In healthy adults, the effects of immediate-release cyclobenzaprine generally subside within six hours of the last dose, she says. “However, this duration is much longer in older adults, who should be started on a lower dose and titrated slowly to avoid excessive side effects.”

How long does cyclobenzaprine take to work?

Cyclobenzaprine doesn’t provide immediate pain relief, according to Dr. Saifullah. Still, it reduces muscle spasms and discomfort within about 30 minutes to an hour, adding that peak effects usually occur between three and eight hours. Dr. Jones adds that the drug’s anti-spasm effects may take one to two days to reach full effect.

Dr. Saifullah says it’s often best to take cyclobenzaprine in the evening or before bed to take advantage of its muscle-relaxing effects and avoid daytime tiredness. “You can take it with or without food, but taking it with food improves absorption,” he says.

RELATED: How much is cyclobenzaprine HCl (Fexmid) without insurance?

Cyclobenzaprine side effects

Dr. Saifullah says cyclobenzaprine can make you feel relaxed and sleepy. Its sedating effect is considered moderate, and caution should be exercised when engaging in activities requiring alertness or operating machinery.

The most common side effects of cyclobenzaprine include:

  • Constipation
  • Nausea
  • Fatigue
  • Dizziness
  • Drowsiness
  • Dry mouth

If you experience the following life-threatening side effects, seek medical attention  immediately:

  • Signs of an allergic reaction: Itching, hives, skin rash, or swelling for the tongue, lips, face, or throat
  • Symptoms of CNS depression: Shortness of breath, slow or shallow breathing, feeling faint, confusion, or difficulty staying awake
  • Changes in heart rhythm: Fast heartbeat, feeling faint, lightheadedness, chest pain, difficulty breathing
  • Symptoms of serotonin syndrome: Agitation, anxiety, restlessness, mood changes, disorientation or confusion, loss of muscle coordination, sweating or shivering, flushed skin, fever, hyperthermia (overheating), increased heart rate or high blood pressure, nausea, vomiting, or diarrhea, tremor, muscle stiffness, hyperactive reflexes, dilated pupils

Cyclobenzaprine is contraindicated in the following populations:

Alcohol increases the risk of sedation and should be avoided with cyclobenzaprine. Possible drug interactions that may also worsen sedation include:

How long should you take cyclobenzaprine?

Cyclobenzaprine is typically prescribed for short-term use to manage acute muscle spasms. Long-term use is generally discouraged due to the potential risks of dependence, tolerance, and increased likelihood of experiencing adverse effects, says Dr. Saifullah. Taking it every night isn’t recommended. “You should stop taking it once your muscle spasms and pain have subsided, usually within two to three weeks, he says.

Adhering to the prescribed duration of treatment and consulting with a healthcare professional if concerns arise or if symptoms persist is crucial.


RELATED: Cyclobenzaprine interactions to avoid

Cyclobenzaprine alternatives

In cases where cyclobenzaprine is not suitable or contraindicated, alternative treatment options for managing muscle injuries or spasms may be necessary.

They include medications and dietary supplements, such as:

Dr. Saifullah recommends the following non-pharmacological options:

  • Physical therapy to improve flexibility and strength
  • Applying ice or heat to the affected area
  • Massage to reduce muscle tightness
  • Adequate rest and avoiding activities that might worsen the injury

The bottom line? Cyclobenzaprine provides short-term relief from muscle spasms and injuries. It takes effect in 30 minutes to an hour and lasts four to six hours (immediate-release) or up to 24 hours (extended-release). Consult your healthcare provider to determine the best treatment option for your condition.