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Dr. Rick, MD
Dr. Rick, MD, Board Certified MD
Category: Medical
Satisfied Customers: 10588
Experience:  20+ years as a doctor. Internal Medicine Internship in NYC
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How Long Does Flexeril Stay In Your System?

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How long does flexeril stay in your system for a urine test? Person had surgery in January, takes testosterone 1.5cc every 2 wks and 1 5-325 percocet daily. Took two pills in January. Could you provide some detail of your answer, to give him peace of mind, not just the standard 7 days? Thank you.

You want to know if flexeril would be detectable in urine at this point when the last dose was taken in January? Is that correct?

JACUSTOMER-qfyz691u- :

Actually, not for today, but would it still be detectable 30 days after taking, with the other medications he took?

RickMD :

Is he concerned that any of the other medications, such as percocet, showing up?

JACUSTOMER-qfyz691u- :

No, just the flexeril

RickMD :

Ok. The time that a drug stays in your body, and therefore would be detectable in urine, is based on the drugs "half life".

To be "totally gone" the drug needs to have gone through 5 half lives since the last use.

Does this make sense to you so far?

JACUSTOMER-qfyz691u- :


RickMD :

Flexeril has a half life of 18 hours. So 5x18 is 90 hours. Or just under 4 days.

Of course, it is not that easy. This varies on how much and how long the drug was taken and it can vary from person to person.

That being said I cannot image any way that flexeril would be detectable 30 days after the last dose.

Customer: replied 3 years ago.

300 nano grams are the minimum requirement on the military urinalysis. Will this be detectable with the other medications he is taking, or is 30 days enough time for no trace amount?

That is a very low detection limit. They must be using Mass Spectrometry in their testing. That being said, from his history of using the flexeril at the dosage of two pills the one time in January, I truly believe he will test clean, even at that high tech levels. That is 40 entire half lives. At that point nothing is left in his body at all.

Just to be clear, taking the test 30 days after his last dose calculates out to 40 half lives of the medication and it is known to be gone after only 5. That is a huge safety margin. He has nothing to worry about.

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