What happens to a medication once it’s in my body?

This article was authored in partnership with Prairie Health.

Knowing how your body processes mental health medication can be helpful in understanding your own medication regimen. It can help you feel a sense of control over your treatment and feel more comfortable with taking medication.

Let’s take a look at what happens to a medication once it enters your body.

Medication’s journey in your body

All medications are processed by the body through a 4-step process: absorption, distribution, metabolism, and elimination [1].


The absorption step begins when the medication enters the body and ends when it enters the bloodstream.

Your body can absorb medication in many ways: through the lungs, through the skin, or directly into the bloodstream through injection. However, most mental health medications are taken orally as pills or tablets. The medication moves through the digestive system, where your body breaks it down into smaller pieces. When these bits of medication become small enough, they pass through the lining of your digestive system and are absorbed into the bloodstream for distribution.


In the distribution step, the bloodstream moves the newly absorbed medication throughout the body. Mental health medications generally take effect when they reach the brain.

After taking effect, the medication reenters the bloodstream. Eventually, it passes into the liver.


In the metabolization step, enzymes in the liver process medication in one of two ways.

Some drugs are converted into an active form that the body can more readily use. In this case, the bloodstream once again distributes the altered medication throughout the body so it can have its intended effect.

In other instances, the liver converts the medication into an inactive form that is ready to leave the body.


For most drugs in the elimination step, the remaining medication is sent to the kidneys, where they are filtered into urine and then leave the body.

How Long Medication Stays In Your Body

Most medications have a half-life. The half-life of a medication is the amount of time it takes for half of the medication to exit the body.

For example, the antidepressant duloxetine (brand name: Cymbalta) has a half-life of 12 hours. If you take 20mg of duloxetine at 6:00am, then there will be 10mg left in your body at 6:00pm. By 6:00am the next day, another half of that amount will be processed, with 5mg remaining.

A drug’s half-life is linked to how long it takes to begin working in the body. Generally, the shorter a drug’s half-life is, the more quickly it will take effect.

However, some of these effects are often not noticeable for a longer time. Antidepressants work by altering the concentration of certain neurotransmitters in the brain. These changes build up over time. Antidepressants start working quickly, but many people don’t see improvements in their mood until several weeks until after they start taking them [2]. Because it takes much longer for antidepressants to have their effect than the rate at which they’re broken down, antidepressants are typically prescribed for daily use. Other types of medications (such as some anxiety meds) work more quickly.

(If you’ve been taking a mental health medication for a long time and haven’t seen any improvements compared to when you started, consult your doctor.)

Everyone’s metabolism is different

Throughout this process, there are many factors that affect how your body processes medication. These include your age, your health, and the combination of medications you might be taking. In some cases, different medications, when taken together, can cancel out one another’s effects. (Sometimes doctors take advantage of this by prescribing one medication that reduces the side effects of another medication.)

Another important consideration is genetics. Your genes dictate what kinds of enzymes their body produces. Different forms of enzymes in the liver can cause your body to process a given medication faster or slower than average. For example, if your enzymes metabolize a medication too quickly, then the medication may not stay in your system long enough for it to work properly. On the other hand, if your enzymes metabolize a medication too slowly, the medication may accumulate in your body—which can lead to negative side effects.

What about supplements? Recreational drugs?

Your body processes nutritional supplements and recreational drugs in exactly the same way it process medication. The specifics of each substance are unique—and so is the way each substance affects you. But in general, all supplements and drugs follow the same 4-step process of absorption, distribution, metabolization, and elimination.


When you find the right medication for your mental health condition, the results can feel miraculous—but the process behind how your body processes that medication doesn’t need to be a mystery. Learning what happens to a medication once it’s in your body can help you feel more in control of your treatment.

Further Reading

  1. Susa, S. T. (2021). Drug Metabolism. StatPearls. Retrieved from  https://www.ncbi.nlm.nih.gov/books/NBK442023/
  2. Harvard Health Publishing. (2021). When to expect results from a new medication. Retrieved from https://www.health.harvard.edu/staying-healthy/when-to-expect-results-from-a-new-medication

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