Those who use methamphetamine, or meth, tend to experience the impact of the drug very quickly. The “high” will usually last for a few hours — up to eight — and they may have some residual effects for four hours after that. Of course, it depends on how much they take and other such factors, but this is a general timeline.
However, do not make the mistake of assuming that the drug can’t be detected after 12 hours. This is not like alcohol, where your BAC drops relatively quickly and, if you feel sober, you’d pass a test. You can still fail a drug test for meth for quite a while after use — and that can have serious consequences if you’re accused of a crime. For example, a positive drug test can be used against you if you’re accused of negligent vehicular homicide or something similar.
How long the authorities can detect a drug depends on what type of test they use. Using a blood test, for instance, meth can usually be detected in your system for the next one to three days after use. Blood tests are very common in criminal cases, especially if you wind up in a hospital setting after an arrest. If the authorities use a saliva test instead, the authorities may get an extra day. Detection times generally run from one to three days.
Urine tests may detect the drug in your system even longer, depending on your frequency of use. For light users or someone who just tried meth once, the window is the same as above: One to three days. For heavy users, though, the window of detection increases to as much as a week.
The biggest long-term test available for meth, along with many other illegal drugs, is a hair test. They can find evidence of use for as long as 90 days or about three months. If you have legal complications based on test results that show you were using meth, make sure you are very familiar with your defense options.