Why can you test for drugs in urine? Because the liver breaks them down and then the kidneys remove drugs from the body by expelling them in the urine. There are two things we need to look at here: how are drugs metabolized by the body and what do drug tests test for?
How are drugs metabolized by the body? Drugs all take the same path through the body. The first step for any drug is to get it into your blood. Drugs affect our brains in some way, which is why people want to take them. Drugs can be taken orally, injected, snorted up the nose, or inhaled. Each method puts the drug into the blood. The oral method is the slowest of all of these because the drug has to be absorbed through the intestine first. Snorting the drugs puts them into the veins that are in the nasal tissue inside the nose. This is faster than an oral dose. Injecting and inhaling are both much faster and pretty much as fast as each other. Inhaled drugs pass into the blood through the lungs and injected drugs are injected directly into a vein.
Once the drugs are in the blood, they have to get to the central nervous system. To do this, they need to cross the blood-brain barrier, which is not easy to do because it is made of tightly woven capillaries that are there to stop foreign objects getting to the brain from the blood. Once the drug is in the brain, it will have whatever effect it is designed to have, and the moment where it crosses the blood-brain barrier is usually where the rush comes from.
As the drugs go round in the blood, they have to pass through the liver and this is where they are broken down. Drugs taken orally go from the intestines, through the liver and into the blood, so they have already been partially metabolized when they hit your system. That is why ingested drugs take longer to have an effect and the effect is usually less than inhaled or injected drugs.
How does the liver break down the drugs? Different drugs are broken down in different ways, but all of these methods use enzymes. An enzyme is a protein that is a biological catalyst, which means it can start a chain reaction. In the liver, most drugs are broken down by an enzyme called cytochrome P-450. These enzymes can start the chain reactions that can convert the drugs into another substance. If the drug is an active drug, the enzymes will convert it into an inactive form, called a metabolite. Sometimes, drugs are designed that begin with an inactive form, but the enzymes in the liver convert them to an active form and then they carry out whatever they were designed to do on the body before the liver converts the active version to an inactive one. All drugs have a half-life, which is the amount of time it takes the liver to reduce the quantity of active drugs by half. For example, heroin has a half-life of 30 minutes and cocaine has a half-life of about one hour.
Once the drugs have been broken down into less harmful metabolites, they are sent to the kidneys, via the blood, in the form of urea. The kidneys filter the urea out of the blood, add water, and that is excreted as urine.
So, what does a urine drug test look for? Every drug that is metabolized by the liver is broken down into a metabolite that is a specific chemical. For example, cocaine is broken down into benzoylecgonine and heroin is metabolized into 6-monoacetylmorphine and morphine, which is then broken down further. These chemicals are passed in the urea to the kidneys, where they are urinated out. The urine drug test looks for traces of the drug itself or for the metabolites, which are proof that the drug was in the system. And, just because the half-life of a drug is low, it doesn’t mean the drug will be out of the body quickly. It will be broken down, but it will take a while to be excreted. Cocaine can be tested for up to 7 days after it has been taken and heroin up to 10 days. Alcohol can be tested up to 5 days later and marijuana hangs around for up to 6 weeks.
Urine tests are not the only way to see if someone has been taking drugs. A blood test is an excellent method, but you can also test feces. Drugs can also be passed by the liver to the digestive tract through bile. They are then excreted out. Drugs are also passed through the lungs, breast milk, sweat, saliva, and tears. When someone smells drunk the morning after, it is because the alcohol is being excreted through the sweat glands and being breathed out.
So, how can you test for drugs in urine? The liver breaks them down into recognizable chemicals that are excreted out by the kidneys. The drug test looks for these chemicals. And that is what I learned today.
Sources
https://organicindiausa.com/blog/liver-and-kidney/
https://www.aruplab.com/files/resources/pain-management/DrugAnalytesPlasmaUrine.pdf
https://sunrisehouse.com/addiction-info/path-drugs-take-body/
https://www.kidney-international.org/article/S0085-2538(15)32394-2/fulltext
https://www.msdmanuals.com/en-jp/professional/clinical-pharmacology/pharmacokinetics/drug-metabolism
https://www.medicalnewstoday.com/articles/how-long-does-cocaine-stay-in-your-system#how-long
https://www.medicalnewstoday.com/articles/how-long-does-cocaine-stay-in-your-system#how-long
https://www.msdmanuals.com/en-jp/home/drugs/administration-and-kinetics-of-drugs/drug-elimination