system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the difference between Advil, Tylenol, and aspirin? I know they're different drugs, but what is each one doing to my headache/ pain?
gpt
Advil is ibuprofen, and Tylenol is paracetamol, for those unfamiliar. Both are proprietary brand names. 

Ibuprofen and asprin are both considered Non-Steroidal Anti-Inflamatory Drugs (NSAIDs). Paracetamol isn't, but at the same time it kind of is- the mechanism is very similar, but it isn't very effective at being an anti-inflammatory.

All three act in pretty much the same way- they inhibit an enzyme (COX, paracetamol being very selective for COX-2) that is involved in a cascade of molecules that operate the pain pathways. The exact mechanisms are unclear though.

The ELI5 explanation is that basically they all do pretty much the same thing for your headache, but they all have different other effects elsewhere in the body, which is why people take ibuprofen when they've sprained their ankle, but not paracetamol.