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How Long Does Flexeril Stay in Your System?

Flexeril, also sold under the generic name cyclobenzaprine or brand name Amrix, can stay in your system for an extended period of time. The potent central nervous system (CNS) relaxant is only intended to be used for two to three weeks. However, it is sometimes prescribed for longer periods to treat various musculoskeletal conditions and fibromyalgia. It’s often misused or abused as well.

Experts say the medication is not addictive. Even still, withdrawal-like symptoms may occur when it’s taken for more than a couple weeks. Nausea, headache, and general discomfort commonly occur in these situations. Doctors usually have patients taper off the medication as a result.

Despite this, nearly 30 million people are prescribed cyclobenzaprine each year. If you’re one of the millions taking it, you may wonder how long Flexeril stays in your system. 

The answer is not the same for everyone and depends on:

  • Frequency of use. The more you take, the more it builds in your system.
  • Duration of use. Due to its extensive half-life, long-term use causes build-up too.
  • Dosage. Higher doses and extended-release versions take longer to metabolize.
  • Genetics. Some people naturally metabolize it faster or slower.
  • Age. Flexeril has not been tested on children under age 15. Older adults may metabolize the drug slower.
  • Weight. It typically takes heavier people longer to excrete the drug.
  • Metabolism. Variations in metabolism impact how the body breaks the medication down.
  • Other factors. A variety of individual factors impact how long Flexeril stays in your system.

Details on how long it lasts under various conditions are outlined in greater detail below.

How Long Does Flexeril Stay in Your Body?

There are immediate-release and extended-release versions of Flexeril. Both begin working in as little as one hour and peak in about 7-8 hours. The effects can last anywhere from 12-24 hours after the last time taken.

Effects Last Approximately 12-24 Hours

During this phase, the most common body and brain effects people experience include:

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

More severe symptoms can occur too, and these can sometimes signify an overdose that warrants immediate medical assistance.

The Half-Life is 8-37 Hours

The immediate-release variety has a half-life of 8-37 hours. It comes in 5 mg, 7.5 mg, and 10 mg tablets. This in mind, it could take the body 37 hours to reduce a 10 mg dose to 5 mg in your body.

The extended-release has a half-life of 32-33 hours. It comes in 15 mg or 30 mg capsules. It could take the body 33 hours to reduce a 30 mg dose to 15 mg in your body.

That said, the average half-life is 18 hours overall and most people take the 5 mg dose. If it was only taken once, an average person would have 2.5 mg in their body at 18 hours. At 36 hours, there would be 0.75 mg. The catch is, most people are directed to take the medication three times per day.

Flexeril builds up in your body quickly. Within three or four days of regular dosing, the amount retained in your plasma is roughly four-times more than a single dose. This is why the amount being taken and the length of time taken has such a profound impact on how long it stays in the body.

How Long Does Flexeril Stay in Lab Tests?

Most lab tests aren’t screening for Flexeril. It’s not even usually part of a comprehensive 12 panel drug test. However, employers can pick and choose which substances to screen for. Some may specifically look for cyclobenzaprine. This is more common when drowsiness or disorientation in the workplace poses a safety risk. Doctors may order lab tests to check for it as well.

The window in which the medication might show up in a drug test varies on the type of screening performed. 

How Long Does Flexeril Stay in Your System?

  • Urine tests
  • Hair tests
  • Blood tests
  • Saliva tests

How Long Does Flexeril Stay in Your Urine?

Flexeril stays in your urine for three to eight days. The wide variance is due to differences in the individual, the long half-life, and other factors.

It’s also worth noting that the molecular structure of Flexeril closely resembles tricyclic antidepressants (TCAs). This includes older antidepressants like amoxapine and doxepin. Because of this, Flexeril is frequently mistaken for a TCA in urine tests.

How Long Does Flexeril Stay in Your Hair?

Hair drug tests can provide a 90-day history of drug use. This is because biomarkers of drugs become entrapped in hair as it grows. It also means that it may take several days or even weeks for a substance to be detectable in hair testing.

That said, Flexeril is rarely screened for via hair tests. Most hair tests screen for things like amphetamines, cocaine, opiates, marijuana, and PCP.

How Long Does Flexeril Stay in Your Blood?

Flexeril stays in your blood for three to eight days. Again, the half-life can be anywhere from 8 to 32 hours and it builds up in your system over time. This makes it somewhat difficult to predict.  

How Long Does Flexeril Stay in Your Saliva?

Flexeril usually only stays in your saliva for up to 36 hours. However, the window may extend an additional two days depending on the extent of usage.

Get Help Quitting Flexeril

Even though Flexeril is not considered addictive, its misuse or abuse can cause serious issues. On the one hand, taking it for anything more than a two or three weeks and stopping without tapering can result in withdrawal-like symptoms.

Flexeril is also routinely used for recreational purposes. It may be mixed with other drugs, including addictive substances. It has the tendency to enhance the effects of alcohol, barbiturates, and other central nervous system depressants. This can result in life-threatening interactions.

If you or a loved one wants to stop using Flexeril, get the support you need. Contact a local treatment center for help.

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