“What’s the difference between ibuprofen and aspirin, and when should I take which?”

—Alyssa O., California State University, San Bernardino

Here’s what I generally recommend to students:

  • Go to school with ibuprofen (instead of aspirin)
  • Keep a supply of acetaminophen too (Paracetamol and Tylenol are common brands)

To see why, read on.

Aspirin and ibuprofen do have quite a lot in common—I think of them as close cousins.

Aspirin is salicylic acid, a naturally occurring substance that Native Americans used to extract from willow bark. It’s an analgesic (meaning it blocks pain) and anti-inflammatory. It also inhibits platelets in the blood from clumping together. This can be a benefit, as when it decreases the risk of a blood clot after a heart attack or surgery. Aspirin can also be a risk, as it can lead to gastrointestinal (GI) bleeding (more commonly in the elderly).

Ibuprofen is a synthetic molecule based on the chemical structure of aspirin. It was originally a prescription medication, but proved safe enough that it went over-the-counter in the early 1980s. Ibuprofen is widely available in both name-brand and generic forms, as well as in combination with antihistamines or decongestants designed to treat colds or the flu. Ibuprofen shares many of the same risks as aspirin: Overuse can lead to GI bleeding or kidney damage. Occasional use, though, is generally safe. The over-the-counter doses are 200 mg a pill, which allows some flexibility in dosing.

Aspirin and ibuprofen are both useful medications for treating common pains (headaches, sore throats) and inflammation (ankle sprains). They also work nicely for the woozy headache one can get after sun overexposure.

I generally recommend ibuprofen instead of aspirin because aspirin carries the potential risk of a rare but serious condition called Reye’s syndrome. This can occur when a person under 18 takes aspirin while infected with the influenza virus (flu). Because the risks and benefits of aspirin and ibuprofen are similar, I keep it simple and recommend ibuprofen.

Acetaminophen isn’t an anti-inflammatory like ibuprofen or aspirin, so it’s not as good for musculoskeletal injuries. On the upside, it doesn’t have the risk of GI bleeding or kidney injury. It can cause liver injury if overused. The mechanism of action is different enough from aspirin and ibuprofen that it’s useful to have acetaminophen on hand too. Some pain responds better to one than the other.