How Long Will You Test Positive For Methamphetamine?

In our latest question and answer, the pharmacist discusses how long methamphetamine is detectable on a standard drug urinalysis test.

Question

If I were a heavy meth user and I haven't used for 10 to 15 day, could I start a colon and liver detox 2 or 3 days in, then get a urine screen and test positive? Is it common or possible that it's from my prior use and that the detox brought it out from being stored in my liver or fat anywhere?

Asked by Vinny On Jun 07, 2018

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Jun 07, 2018

MethamphetamineThe approximate detection time for methamphetamine (or amphetamine which is an active metabolite of methamphetamine metabolism) is 2 to 4 days based on the Center for Substance Abuse Treatment urine collection and testing procedures. However, there are several factors which can alter how long it lasts in your body such as:

  • Weight
  • Hydration status
  • Urinary pH
  • Body fat
  • Length of use


Methamphetamine Metabolism And Drug Screening

Methamphetamine is mostly metabolized by the liver, with metabolism producing at least 7 metabolites, including:

  • Amphetamine
  • 4-hydroxymethamphetamine
  • 4-hydroxyamphetamine
  • 4-hydroxynorephedrine


The reported half-life (time it takes for the body to metabolize and eliminate 50% of a drug) of methamphetamine varies widely by source. The prescribing information for an oral methamphetamine product, Desoxyn, lists a half-life of 4 to 5 hours. Various studies however, report a longer half-life, between 15.9 and 22 hours. In addition, amphetamine, a metabolite of methamphetamine, has a reported half-life between 9 and 14 hours.


It generally takes around 5 to 6 half-lives for methamphetamine to be no longer detectable on urine drug screens. Assuming a half-life between 15.9 and 22 hours, this lines up with the published data from the Center for Substance Abuse Treatment, that methamphetamine will only be detectable for 2 to 4 days.


Now, as mentioned above, there are several factors that can affect how long methamphetamine is detectable in the urine. One of the main factors is urinary pH, or the acidity of your urine. Alkaline urine will significantly increase the half-life of methamphetamine, meaning it will be detectable for longer periods of time. Various food and drink can cause urine to be more alkaline, including:

  • Certain fruits (e.g. apples, avocados, cherries etc...)
  • Certain vegetables (e.g. carrots, beans, peas)
  • Nuts
  • Dairy products (due to the calcium content)


Acidic urine will significantly decrease the half-life of methamphetamine, making it detectable for shorter periods of time. Acidic foods include:

  • Certain vegetables (e.g. corn)
  • Certain fruits (e.g. prunes, blueberries)
  • Beef
  • Certain types of fish (e.g. salmon)
  • Certain grains (e.g. wheat, oat, barley)


Using a drug detox product for methamphetamine, could presumably cause changes in urinary pH, which will affect clearance of the drug.


Lastly, methamphetamine is lipophilic (i.e. "fat loving"), and can store in fat cells with chronic use, lengthening detection times. Although uncommon, methamphetamine has been detected in the urine of chronic users 1 to 2 weeks after last use according to studies

About the Pharmacist

Dr. Brian Staiger Pharm.D

Dr. Brian Staiger is a licensed pharmacist in New York State and the founder of PharmacistAnswers.com. He graduated from the University At Buffalo with a Doctor of Pharmacy degree in 2010. He has been featured in numerous publications including the Huffington Post as well as a variety of health and pharmacy-related blogs. Please feel free to reach out to him directly if you have any inquiries or want to connect! He's answered thousands of medication and pharmacy-related questions and he's ready to answer yours! Brian.Staiger@PharmacistAnswers.com Office: 716-389-3076

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