Cyclobenzaprine and Flexeril are the same medication. Cyclobenzaprine is the generic (chemical) name, and Flexeril is the brand name originally given to the drug by its manufacturer. If your pharmacy fills a prescription for Flexeril with a bottle labeled “cyclobenzaprine,” you’re getting the identical active ingredient at the same strength.
Why You Might See Different Names
Flexeril was the original brand-name product, available as immediate-release tablets in 5 mg and 10 mg strengths. The brand-name version has since been largely replaced by generic cyclobenzaprine, which is widely available and significantly cheaper. You may still hear doctors or pharmacists use “Flexeril” as a shorthand, much like people say “Advil” when they mean ibuprofen.
There’s also an extended-release capsule form of cyclobenzaprine that was sold under the brand name Amrix, available in 15 mg and 30 mg doses taken once daily. A sublingual (under-the-tongue) tablet form exists as well. All of these contain cyclobenzaprine as the active ingredient; they just differ in how the drug is delivered and how often you take it.
What Cyclobenzaprine Does
Cyclobenzaprine is a muscle relaxant prescribed for short-term relief of muscle spasms, typically from acute injuries like a pulled back or strained neck. It works in the brain rather than directly on your muscles. The drug reduces signals from the brainstem that keep muscles in a tense, contracted state, which is why it eases spasms without making your muscles feel weak or floppy.
Its structure is closely related to older antidepressants called tricyclics, which explains some of its side effects and drug interactions. It’s not a painkiller on its own, but by calming the spasm cycle, it often reduces the pain that comes with it.
Common Side Effects
Drowsiness is the most frequent side effect, reported by up to 38% of people who take it. Dry mouth is nearly as common, affecting up to 32%. Dizziness occurs in 1% to 10% of users. These effects tend to be more pronounced when you first start taking it and often improve after a few days.
Because drowsiness is so common, most people are advised to take their dose at bedtime, especially at the start. The sedation can actually be helpful if muscle pain is keeping you awake, but it can impair driving and reaction time during the day.
How It Compares to Other Muscle Relaxants
Cyclobenzaprine has been studied in more clinical trials than any other muscle relaxant, and it consistently performs better than placebo for acute back and neck pain. A large systematic review found fair evidence that cyclobenzaprine, along with a handful of other muscle relaxants, is effective for musculoskeletal conditions, but no clear evidence that any single one works better than the others. The choice between muscle relaxants often comes down to side effect tolerance, how sedating the drug is, and individual response.
Important Safety Considerations
Cyclobenzaprine is not safe for everyone. It’s contraindicated for people in the acute recovery phase after a heart attack and for those with arrhythmias, heart block, conduction disturbances, or congestive heart failure. This ties back to its structural similarity to tricyclic antidepressants, which can affect heart rhythm.
The drug also carries a risk of serotonin syndrome when combined with medications that raise serotonin levels, including many common antidepressants. Serotonin syndrome causes symptoms like agitation, rapid heartbeat, high body temperature, and muscle twitching, and it can become dangerous. If you take an antidepressant, your prescriber needs to know before starting cyclobenzaprine.
Older adults are typically started at a lower dose (5 mg) because the drug’s sedating effects and its impact on balance can increase fall risk. People with liver problems may also need a lower starting dose, since the liver is responsible for breaking the drug down.
Typical Dosing
The standard immediate-release dose for most adults is 5 mg taken three times a day, which can be increased to 10 mg three times daily based on how well it works and how well it’s tolerated. The maximum is 30 mg per day at the higher dose. Extended-release capsules are taken once daily, usually 15 mg, with the option to increase to 30 mg. The sublingual tablet starts at 2.8 mg at bedtime for the first two weeks, then increases to 5.6 mg.
Cyclobenzaprine is designed for short-term use, generally two to three weeks. Muscle spasms from acute injuries typically resolve in that window, and the drug hasn’t been well studied for longer courses.