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Dear Dr. Ken: I read your recent article on the risks associated with long-term pot use and am hoping you could help me out with a problem -- (no, not manboobs) concerns about drug testing.

Could marijuana be detected in someone's system during a yearly physical or doctor's visit? How long does marijuana stay in someone's system before it doesn't show up on a drug test? Is there any pill I can take that will mask the marijuana and keep me from failing the test? -- Thank you, Floyd P.

Dear Floyd: Drug testing is a complex subject which most people, including most doctors, don't know much about. While there are a variety of ways to test for use of illegal drugs. Urine testing is by far the most common and it typically checks for the following: marijuana, cocaine, opioids (heroin, oxycontin, etc.), amphetamines and PCP.

Dr. Ken clears up some of the cloudiness surrounding testing urine for drugs after the jump.

Yearly Physical Urine Tests: The type of urine test used when you have a routine physical at your doctor's cannot indicate anything at all about pot smoking. Generally, the only situations where you might undergo drug testing is a work-related evaluation (such as a pre-employment physical) or if you are brought into an emergency room unconscious without explanation, acting strangely, or if there's a question if drugs played a role in an accident or injury.

Gunking Up the System: The more you smoke, the longer it hangs around. Regular pot smokers will have detectable levels in their urine for up to seven weeks after they stop using. Occasional smokers (for example, one joint once or twice a year) will have detectable levels of pot in their urine for about a week.

Washing it Away: Most of the ads for products claiming to fool the test are only trying to fool you. Some efforts are quite extreme (check out the Whizzinator). Nonetheless people try to get around it. The two most common tactics are:

Dilution: Drinking large amounts of water or juice, and hoping to the test won't be able to detect small traces of pot. Sometimes people even add tap water into the cup. These strategies are almost certain to fail as excessive dilution is one of the easiest thing to assess. What's more, the urine would have to be so diluted to fool the test that it would have lost its yellow coloring, immediately raising suspicion.

Substitution: Getting your non-stoner friends to fill a cup full of urine that you bring with you and then dump in the cup. Unfortunately, you can't bring anything with you into the test bathroom. Even if you could, the temperature of recent pee would be close to body temperature while pee that is sitting around a while is closer to room temperature. That 25 (or so) degree difference will be noted as temperature is part of the assessment.

Reasonable and Unreasonable Excuses for Testing Positive for Marijuana Reasonable: Ingesting hemp products, particularly hemp seed oil, can falsely cause a test to signal marijuana.

Unreasonable: Don't embarrass yourself by saying you were hanging around people who were smoking but that you did not use it yourself. Second-hand pot smoke does not accumulate in the urine to a level that is anywhere near detectable levels. Don't bother looking baffled by a positive test--the urine test is rarely wrong. Additionally, positive samples are then sent for more sophisticated testing to confirm the result. Both tests being mistaken is unheard of.

If you opt out

Refusing to provide a sample (i.e. refusing to pee in the cup) for a pre-employment drug test is considered equivalent to finding drugs in your urine. Claiming you can't pee under pressure or on command (aka "shy bladder") requires verification by a doctor.

Dr. Ken Spaeth is a Harvard-trained physician and a clinical instructor at Mount Sinai School of Medicine in New York . He is also co-author of the "Bioterrorism Sourcebook." You can e-mail him your questions at askdrken@aol.com.