Nobody Knows How Tylenol Works

TL;DR

Acetaminophen has been used by billions for over 70 years, yet scientists still have no confirmed explanation for how it relieves pain.

Key Points

• 1.Acetaminophen was discovered entirely by accident in 1884. Physicians Arnold Khan and Paul Heep accidentally received acetanilide instead of naphthalene from a pharmacy, and noticed it reduced fever — a completely unexpected effect.
• 2.The drug reached 79% of the American population by 2016 without anyone knowing its mechanism. Tylenol launched in 1955 and is now an active ingredient in over 600 medicines with a $9.5 billion global annual market.
• 3.Tylenol is definitively not an NSAID like ibuprofen. Unlike ibuprofen, it doesn't cause stomach irritation or reduce inflammation, suggesting it doesn't inhibit COX-2 enzymes throughout the whole body the way ibuprofen does.
• 4.The leading theory is that Tylenol inhibits COX enzymes only in the brain and central nervous system. It may only function in low-peroxide environments like the brain, but exactly how it's restricted there remains unknown.
• 5.Alternative theories involve cannabinoid neurotransmitters and serotonin, but none are confirmed. Scientists speculate Tylenol may interact with the same pathways activated by cannabis or the 'happy hormone' serotonin, yet no consensus exists.