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Detection Time of Methamphetamine: Compared to cocaine, methamphetamine’s effects can be more intense and last longer. The half-life for methamphetamine (the time period required for the body to decrease the blood level of methamphetamine by 50%) ranges from 6- 20 hours.

The time window for detecting methamphetamine will depend on both testing factors and individual factors. All screening and quantitative tests have a lower limit, or cut-off, for detection. This limit varies for tests and among labs. If a person had used methamphetamine many hours prior and the concentration was very low in the blood or the urine, a qualitative test may come back as negative. Quantitative tests may also result in negative results if the amount in the sample was below the lab threshold for a positive report. Very sensitive tests, with much lower cut-offs for concentrations, will detect the presence of methamphetamine and amphetamine sooner and for a longer period of time than less sensitive tests. Laboratories will inform you of the lower limits by either including the cut-off level on the written report or through a personal communication.

The method by which methamphetamine is consumed will also impact detection time. Intravenous use will have almost immediate detectable methamphetamine in blood samples and in the first void after use. Oral ingestion of methamphetamine requires absorption through the GI tract and requires a longer period to detect the drug. Peak blood levels occur three hours after an oral dose. Urine tests may require 12 to 24 hours to test positive.

The duration of detectable of methamphetamine and amphetamine in blood or urine can vary due to several factors. The half-life will be shorter if a person has acidic urine; the kidneys will clear the drug faster when urine is acidified. This has led to the marketing of acidifying products, such as vitamin C supplements, to people anticipating a urine drug screen.

An individual may have impaired liver function or take medications that block the metabolism of methamphetamine by enzymes in the liver. Medications that inhibit the liver’s P450 enzyme system and slow the metabolism of methamphetamine to amphetamine are called P450 inhibitors and include common over the counter and prescribed medications such as the antidepressant Prozac and the sleep  and allergy aid diphenhydramine.


This month’s criminal topic is the Methamphetamine Toxicology. Topics covered are:

  • What will trigger a drug screen (6/2/16)
  • Screening for Meth (6/9/16)
  • Blood Toxicology (6/16/16)
  • Detecting Meth (6/23/16)

Note: To see all posts in this topic, click here.

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