Medicine can help you fight off an illness, keep you from getting sick, or make you feel better. For example, if you’ve ever been sick and had a headache, you might have taken a pill to make the pain go away. Have you ever wondered, how do pills know where to go in your body to treat the pain you're feeling?

It turns out that pills actually don’t know where to go! Pills are small tablets that contain medicine, or specific molecules. When you swallow a pill, the medicine goes into your digestive system before making it into your circulatory system, where it is carried in your blood all around your body. So pills go everywhere, not just to the location where you’re feeling a symptom like a headache.

However, the only place that pills do their job is where you feel the ache. Scientists design medication to only interact with specific molecules in the body. These molecules are proteins that are called “target molecules” or “receptors.” A common way to understand the interaction between medication and its receptors is to think of it like a tiny lock and key. The medicine is like a key, and the receptor is like a lock. Just like a key will only fit into its matching lock, medicine will only interact with receptors that they fit with.

In the example of the headache, one medication you might take is ibuprofen. Ibuprofen fits with certain receptors and stops them from creating prostaglandins. Prostaglandins are molecules that are part of the body’s normal immune response, but they also cause a throbbing feeling. When ibuprofen inhibits these receptors, the pain of a headache subsides.

To put everything together, the medicine in pills makes it to your circulatory system, is carried all around the body, and will only do its job in locations with specific molecules it is meant to work with. Many medications work in the same way, only interacting with specific receptors involved with certain symptoms.

Medicine works the best and is the safest when it's taken in the right amount. Because of this, it’s very important to take medication the exact way that doctors and other adults recommend.