SHEET /vs/diphenhydramine-vs-cetirizine · COMPARISON
Diphenhydramine vs Cetirizine: what is the difference?
How they differ
These are the first and second generation antihistamines, and the difference is whether the molecule reaches the brain. Both block the H1 histamine receptor, which is what stops the itching and sneezing of an allergic response. Diphenhydramine is small and fat-soluble enough to cross the blood-brain barrier freely, which is why it causes strong drowsiness and why it is sold as a sleep aid as well as an allergy medicine. Cetirizine carries a carboxylic acid that keeps it largely out of the brain, so it is much less sedating while blocking the same receptor in the body. Cetirizine also lasts far longer, which is why it is a once-daily product and diphenhydramine is not.
Side by side
| Diphenhydramine | Cetirizine | |
|---|---|---|
| Formula | C17H21NO | C21H25ClN2O3 |
| Molecular weight | 255.35 g/mol | 388.9 g/mol |
| Family | Over-the-counter medicines | Over-the-counter medicines |
| Everyday group | OTC medicine | OTC medicine |
| Functional groups | Aromatics, Ethers | Carboxylic Acids, Aromatics, Ethers, Halogenated |
| GHS signal wordThe supplier-filed hazard label, not a statement about ordinary use. | Warning | Warning |
| Oral LD50A single acute animal measure. It ranks nothing about human safety. | 500 mg/kg (oral, rat) | not recorded |
| Also sold as | Benadryl, ZzzQuil, Sominex | Zyrtec |
| CAS number | 58-73-1 | 83881-51-0 |
| PubChem CID | 3100 | 2678 |
Common questions
- What is the difference between Diphenhydramine and Cetirizine?
- These are the first and second generation antihistamines, and the difference is whether the molecule reaches the brain. Both block the H1 histamine receptor, which is what stops the itching and sneezing of an allergic response. Diphenhydramine is small and fat-soluble enough to cross the blood-brain barrier freely, which is why it causes strong drowsiness and why it is sold as a sleep aid as well as an allergy medicine.
- Is Diphenhydramine bigger than Cetirizine?
- Cetirizine is the heavier molecule, 388.9 g/mol against 255.35 g/mol for Diphenhydramine. Diphenhydramine is C17H21NO and Cetirizine is C21H25ClN2O3.
Read the full records: Diphenhydramine and Cetirizine.