Dr. Dean

Drug Testing: The Half-Life Of Marijuana

Posting Date: 01/14/1999

How unfair can we be when it comes to drugs? I deplore drug abuse, so don?t get me wrong. But the way we deal with the problem of drugs is so unfair.

We talked yesterday about how selective we are when it comes to enforcing drug laws ? and how many more people of color are being tested, overdosing, and going to jail.

Here?s a new study on marijuana excretion. How long does it takes for marijuana to leave your system and not show up on a drug test?

Researchers studied prisoners and classified them as either occasional (once a week) or frequent (more than once a week) users.

In the infrequent users, the half-life of marijuana was 1.3 days. That means it took 1.3 days for the amount of marijuana in their blood or urine to go down 50 percent.

For frequent users, the half-life was one to 10 days.

Then researchers continued to collect up to five urine samples per day until the urine test was negative for marijuana.

For infrequent users, the time from the last reported drug use until the last positive specimen was five to 12 days. Frequent users took 22 to 27 days to clear their systems.

Many of the 21 volunteers had big gaps in their test results. They would have one or two negative specimens and then get a positive result.

That means you could go away on your honeymoon, smoke a joint, come back to work, take a drug test, and get fired. Is that fair?

Source: Forensic Drug Abuse Advisor 1998;10;10:78-9