Here’s a video that explains the exact chemistry behind caffeine, which is the world’s most popular drug.

How does caffeine affect your brain?

Well, when ingested, caffeine breaks up into three different metabolites, each of which has a different effect on the brain. Caffeine can influence everything from increasing oxygen flow to accelerating fat breakdown, which enhances athletic performance. Doesn’t sound too bad?

But the explanation also comes with a downer for caffeine addicts: Scientists have determined that 400mg — or roughly three eight-ounce cups of coffee — is the safest daily intake for adults. What happens when you take more? Find out by watching the video below.