Flexeril, the brand-name version of the drug Cyclobenzaprine, is a muscle relaxant medication with an antidepressant activity used for the treatment of painful muscle spasms and other musculoskeletal conditions. Cyclobenzaprine muscle-relaxing effects are felt within about half an hour of administration, and the drug starts to be detectable in urine, blood, hair, and saliva within a few hours.

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This article focuses on Flexeril half-life, how long it stays in the system, variables that can affect that, Cyclobenzaprine drug tests, and ways of treatment or how to get it out of the body safely.


Flexeril actively works on the muscles for four to 24 hours, depending on the formulation taken.


How Long Does Flexeril Stay In the System?

There are many influencing factors that could affect how long Flexeril stays in the system. But for most users, and with Flexeril half-life of 18 hours considered, getting the drug out of the body will take 4 to 5 days after the last dose was taken. However, it is important to note that its elimination half-life can range from 8 to 37 hours. That said, it may just take 1.83 days for some to eliminate the drug or up to 8.48 days for others.

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Cyclobenzaprine Drug Test

For Flexeril to be detected, the testing kit would have to specifically be a Cyclobenzaprine drug test. It won’t be detected on a standard 12-panel drug test as it is not visible on regular blood, saliva, or urine tests. However, it does have a very similar structure as tricyclic antidepressants, and hence, it can be detected as an antidepressant drug and trigger a false positive. 12-panel drug tests vary in terms of what drugs they search for, though, so Cyclobenzaprine will only show up if a specific test is carried out for that. And even then, it will only show up as a TCA.

Variables That Affect How Long Flexeril Stays In System

Just like other drugs and medications, variables such as age/sex, body mass, metabolic rate, genetics, health condition, frequency of administration, dosage, as well as co-administered drugs affect the length of time Cyclobenzaprine stays in the body. Discussed below are the roles these variables play.

Age / Sex

Aging naturally slows down metabolism. A younger individual may expect to get cleared of Cyclobenzaprine traces in usually 4 days. For elderly individuals, contrarily, it can take longer – usually twice as long – for the drug to process out of the body. With old age comes slower metabolism and overall poorer physiological function, so drugs are emitted much slower as they tend to linger longer in their system. It has also been found that the drug’s steady-state plasma concentrations were twice as high in elderly individuals as in younger individuals following the same oral doses of 5mg.

Body Mass

Weight also impacts the speed of eliminating the drug out of the system. Larger individuals have larger systems, and it helps metabolize Flexeril with more efficiency, so they are able to flush it out faster than smaller ones due to the latter’s smaller systems. The amount of body fat an individual has also plays a role here, and a higher body fat percentage helps speed up elimination.

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Metabolic Rate

Metabolic rates are relevant in this case, too. Fast metabolizers eliminate Flexeril faster and more efficiently than slow metabolizers. While metabolic rates do not usually play a significant role in drug elimination, they still may have a small impact.