There are plenty of reasons that you might be asked to submit to a drug test — to get a job or to qualify for state welfare programs, for example — but critics argue that drug testing raises ethical and scientific concerns. They cite the fact that relatively harmless drugs such as marijuana stay in your system much longer than so-called hard drugs, such as heroin and meth, as well as prescription drugs.

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The differences in detectability for certain drugs is just one of several arguments against drug testing. States are increasingly legalizing marijuana, and that presents a risk of losing out on employment opportunities or federal financial aid because of a positive THC urine test, especially when you compare marijuana's detectability to that of other federally controlled substances.

Here's how long it takes for these six drugs to leave your system.

1. Xanax

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Blood: Two to three days.

Urine: Three to six weeks.

Hair: Up to 90 days.

2. Vicodin

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Blood: Six to eight hours.

Urine: Two to three days.

Hair: Up to 90 days.

3. Marijuana

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Blood: Up to two weeks.

Urine: Seven to 30 days.

Hair: Up to 90 days.

4. MDMA

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Blood: One to two days.

Urine: Three to four days.

Hair: Up to 90 days.

5. Ritalin

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Blood: Around 12 hours.

Urine: One to three days.

Hair: Up to 90 days.

6. Methadone

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Blood: Three to four days.

Urine: 24 to 36 hours.

Hair: Up to 90 days.

Source: Drug and Alcohol Information and Support

With the exception of marijuana and MDMA, this list includes the names of commonly prescribed pharmaceuticals that chemically resemble, or mimic the effects of, hard drugs (e.g. Adderall and meth) — not the substances that standard drug screening policies routinely test.

Prescription drug abuse is on the rise in the U.S.

The Centers for Disease Control and Prevention declared that America's prescription drug abuse problem reached epidemic levels in 2012, noting that one person dies in the U.S. from an unintentional prescription drug overdose every 19 minutes.

We're also reminded each year of the extraordinary annual death toll from marijuana overdoses: zero.

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