In some cases, a big downer to smoking or ingesting weed - in any form for that matter - is that long after the effect wears off, marijuana metabolites stay in your system. In fact, of all “illicit” - or more accurately "Schedule I drugs" - marijuana remains detectable in the body the longest. As long as two months after use.

The most common way of testing for drug use is to test an individual’s urine – but there are also tests for hair, blood and saliva. The urine drug test is cheaper and has a longer detection time than a saliva test.

ARE THERE ANY RELIABLE BENCHMARKS I CAN GO BY?

Unfortunately, the answer to this question is that there are no set rules to figure out how long after you have smoked your last joint or eaten your last ganja brownie, that this will be detectable via a drug test.

A urine test will show use within 2-5 hours after you ingested marijuana. A saliva test will show THC use within one hour of use, but may then only show positive for 12 hours. Hair tests will show THC use about a week after use and will also test positive for up to 90 days.

There are several factors, beyond frequency of use, that will determine if marijuana metabolites will show up in your system. These include your weight, percentage of body fat and the amount you last used.

However, a very rough rule of thumb is as follows:
- A onetime user may test positive between 1-6 days after use.
- Moderate use may test positive between 7-13 days after use.
- A frequent user may show positive for more than 15 days.
- A heavy user may test positive for 30 or more days.
- Some heavy pot smokers have reported testing positive for as long as 90 days after their last usage.

The most reliable way to find out if you test positive (before the official test) is to test yourself.

THE SCIENCE BEHIND URINE TESTS

Urine tests, which is what the vast majority of people face, actually do not test for THC directly. Instead, they are trying to detect the presence of a chemical called THC-COOH or 9-carboxy-THC. The body’s excretion of 9-carboxy-THC is also influenced by your metabolism, percentage of body fat and moderated by diet and stress.

When you consume cannabis, THC enters your bloodstream and is processed into this new derivative chemical. Urine tests have been designed to detect 9-carboxy-THC because it will only be present if you have already used cannabis.

Drug screenings also have a threshold for measuring THC levels in the body. In general, amounts above 50 nanograms per milliliter are reported as positive.