system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How are drugs developed to target specific areas (pain/allergies/disease). How do you translate scientific body knowledge into a drug that targets that area. And how do scientists determine cross reactions to other drugs or conditions. Do they have to test every combo?
gpt
“Designing” drugs is kind of new. Historically, we found chemicals that did something interesting, then we made chemical modifications to it, or looked for ones with similar shapes and experimented to see if they did something.

Today, we still do that, but we also do things like work out what causes pains or disease and try to make drugs specifically shaped to fit some other molecule, or chemically react with it. A lot of biology involves sort of lock-and-key type situations where a particular shape fits into a protein or something, and some shape change or chemical reaction is the result.

Most drugs are still not “targeted”. They mostly get put into the body until they bump into something they happen to interact with, usually by circulating in the blood. Ideally, a drug only interacts with one thing that causes a problem, and hopefully the body doesn’t break it down into smaller molecules that do something undesirable. This is hard, and some drugs can make people sick because it affects things in addition to the one it is supposed to.

However, a great deal of research is being put into how to get drugs to focus on specific tissues or types of calls (like cancer cells). This frequently involves looking for features that are unique to particular groups of cells and finding away to attach to the drug something that will stick to those cell-specific features (like proteins). This is very hard.

If you take something like ibuprofen, you swallow it, the pill dissolves, it’s absorbed into your blood like nutrients from food, and it swishes around your insides by way of your blood like millions of others molecules. When it happens to brush up against a particular protein  involved in inflammation, it gets wedged in it and prevents it from furthering the inflammation.