SHEET /vs/acetaminophen-vs-aspirin · COMPARISON
Acetaminophen vs Aspirin: what is the difference?
How they differ
Aspirin is the older molecule by a century and the more chemically aggressive of the two. It is acetylsalicylic acid, made by acetylating willow-bark salicylic acid in 1897, and it blocks the COX enzymes irreversibly, which is why a single exposure affects platelets for days. Acetaminophen does not do that at all: it works centrally, has little anti-inflammatory effect, and leaves clotting alone. The table shows aspirin's carboxylic acid and ester against acetaminophen's amide and phenol, which is the structural reason aspirin irritates a stomach lining and acetaminophen does not. Reported oral LD50 in rats is 200 mg/kg for aspirin against 1944 mg/kg for acetaminophen, an unusually wide gap for two drugs sold on the same shelf.
Side by side
| Acetaminophen | Aspirin | |
|---|---|---|
| Formula | C8H9NO2 | C9H8O4 |
| Molecular weight | 151.16 g/mol | 180.16 g/mol |
| Family | Over-the-counter medicines, Non-opioid painkillers | Over-the-counter medicines, NSAIDs, Non-opioid painkillers |
| Everyday group | OTC medicine | OTC medicine |
| Functional groups | Aromatics, Amides, Phenols | Carboxylic Acids, Aromatics, Esters |
| GHS signal wordThe supplier-filed hazard label, not a statement about ordinary use. | Danger | Danger |
| Oral LD50A single acute animal measure. It ranks nothing about human safety. | 1,944 mg/kg (oral, rat) | 200 mg/kg (oral, rat) |
| Half-life | 2 h | not recorded |
| Also sold as | Tylenol | Bayer, Bufferin, Ecotrin |
| CAS number | 103-90-2 | 50-78-2 |
| PubChem CID | 1983 | 2244 |
Common questions
- What is the difference between Acetaminophen and Aspirin?
- Aspirin is the older molecule by a century and the more chemically aggressive of the two. It is acetylsalicylic acid, made by acetylating willow-bark salicylic acid in 1897, and it blocks the COX enzymes irreversibly, which is why a single exposure affects platelets for days. Acetaminophen does not do that at all: it works centrally, has little anti-inflammatory effect, and leaves clotting alone.
- Is Acetaminophen bigger than Aspirin?
- Aspirin is the heavier molecule, 180.16 g/mol against 151.16 g/mol for Acetaminophen. Acetaminophen is C8H9NO2 and Aspirin is C9H8O4.
- Which has the lower reported LD50, Acetaminophen or Aspirin?
- Aspirin, at 200 mg/kg (oral, rat), against 1,944 mg/kg (oral, rat) for Acetaminophen. An LD50 is one acute animal measurement, and the two here were not necessarily measured in the same species, so it is a data point rather than a ranking of how dangerous either is to a person.
Read the full records: Acetaminophen and Aspirin.