Meth is a powerful stimulant drug that causes an energetic high. While the effects of the drug typically last from six to 12 hours, traces of meth stay in the body longer. The amount of time that the drug remains in the body can vary widely depending on the person’s physical characteristics, the average dose of meth taken and the frequency of use.
The average window for detecting methamphetamine in a person’s urine is up to three days. Saliva tests can detect the drug one to two days after last use, and hair tests can identify any meth use in the past three months.
The drug can remain in the body much longer after frequent or heavy meth use, which is common among people with a meth addiction. People who use meth occasionally, or recreationally, usually clear the drug from their system more quickly than a chronic meth user will.
Once it’s ingested, methamphetamine makes its way into your blood, urine, saliva, sweat and hair. Fluid and hair samples can be tested for the presence of meth, though some test methods are more convenient and cost-effective than others.
Methamphetamine Detection Times by Type of Test:
According to a 2004 study published in Therapeutic Drug Monitoring, a blood test can detect a 22 milligram dose of crystal meth two days after a person has been smoking meth. The article stated that the average dose for meth users is 5 to 10 milligrams, but people who are tolerant to the drug often take much higher doses.
Like most drugs, meth can usually be detected in oral fluids, or saliva, for one to two days after a person has used it.
Saliva samples are most often collected by placing an absorbent swab in between a person’s lower cheek and gums. The swab is left in place for a few minutes before the sample is sent to the lab for testing.
Hair provides the longest detection window for methamphetamine. Meth can be detected in hair follicles as soon as seven to 10 days after a person has used it. The substance remains in the hair for up to three months.
Hair tests are typically more expensive than other types of testing, and the results can be controversial. Drugs such as meth, cocaine and opioids tend to bind more strongly to hair with darker pigments, and environmental contamination has been shown to cause false positives.
Hair tests are best suited for detecting heavy meth use. They won’t necessarily pick up on one-time use of the drug.
Urine testing is the most common and cost-effective way to screen for methamphetamine use. Meth and its main metabolite, amphetamine, will show up in urine within an hour of ingesting the drug.
Urine samples collected from occasional meth users will test positive one to three days after last use. A chronic meth user might still test positive seven to 10 days after consuming the drug.
Sweat patches are a less common method of testing for meth use. The patches are usually applied for a week at a time to detect drug use during that period. Methamphetamine can be detected in a person’s sweat within two hours of using the drug.
In a small study that used sweat patches to measure how much methamphetamine is excreted in sweat, none of the participants who took low doses of the drug tested positive when the patches were applied two weeks after last use. One of the participants who took high doses of meth tested positive two weeks later.
Testing the meconium, or the first stool passed by a newborn baby, can reveal that a mother used drugs during the previous five months. The testing method is controversial, however, because drug and pediatric experts report high rates of false positives with the technique, according to a 2008 article by the Los Angeles Daily News.
Methamphetamine drug testing has a potential for false positives — which means people can test positive for the drug even when they haven’t used it.
False positives may occur after people use various prescription and over-the-counter medications, including certain antihistamines, nasal inhalers, cold medicines and antidepressants. A 2013 study in the Journal of Analytical Toxicology found that up to 6 percent of positive urine tests for methamphetamine were caused by prescription or over-the-counter drugs.
The body rapidly absorbs methamphetamine whether it’s smoked, injected, snorted or taken orally. The drug is primarily broken down by the liver. In the liver, part of methamphetamine is turned into amphetamine, a stimulant drug that has a similar chemical structure.
Both methamphetamine and amphetamine are excreted in the urine. The length of time meth remains in the body depends in large part on the drug’s elimination half-life, which is the amount of time it takes for the body to clear half the drug from the bloodstream.
Half-lives are not exact, however, and they can vary depending on many physiological factors. The half-life of meth generally ranges from six to 15 hours.
The acidity, or pH, of a person’s urine can also influence how quickly the drug is excreted. Other factors, including age, weight and overall health, affect how quickly meth is metabolized or eliminated from the body.
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