Even though many public health experts now agree that drug use should not be a punishable offense, the fact is that if you happen to be an Olympic athlete, a government spy, or just the child of ridiculously strict parents, you could be subjected to a drugs test. Failing one of these tests is easier than you might imagine, as many drugs can be detected in a person's urine, blood and hair for some time after the actual effects of these substances have subsided. So even if a few days have passed since a drug was taken, a hell of a lot of biology and chemistry still has to happen before you can give a negative sample.
How drugs get in and out of your system
Once drugs are absorbed into the bloodstream – which can occur via the lungs, the digestive tract, or even a syringe – the only way to get them out is by excretion. Depending on what you’ve taken, some may pass straight through you relatively quickly, coming out in your poop. Much of the rest will eventually be released in your urine and sweat. However, before this can happen, drugs have to be metabolized into water soluble molecules, or metabolites.
This process mostly occurs in the liver, which contains catalysts like cytochrome P450 enzymes that cause drugs to become oxidized. As a result, non-polar molecules – which have no overall charge and are therefore not soluble in water – become negative, much like a drug user on a comedown. Normally, these metabolites will then be ionized as well, ensuring that by the time the liver is through with them, they are well and truly ready to dissolve – just like the ego of someone on LSD.
By this stage, the acute effects of any drug will have worn off, and the soluble metabolites in a user’s system will dissolve into the water in their blood, before being filtered out by the kidneys and excreted as urine. This process can take a while, however, giving drug testers the chance to catch people with drug metabolites in their pee and blood.
Image: The kidneys play an important role in drug excretion, filtering soluble drug metabolites out of the bloodstream so that they can pass out of the body in urine. Ben Schonewille/Shutterstock