SHEET /vs/naloxone-vs-naltrexone · COMPARISON
Naloxone vs Naltrexone: what is the difference?
How they differ
These two are constantly confused, they differ by one small chemical group, and what they are used for could hardly be less alike. Both are opioid antagonists: they occupy the mu-opioid receptor and switch nothing on, which displaces any opioid already there. Naloxone is poorly absorbed by mouth and acts within minutes when injected or sprayed into the nose, which is why it is the overdose reversal agent carried in emergency kits. Naltrexone survives the gut, lasts many hours, and is used to maintain a blocked receptor over time rather than to rescue anyone in an emergency. The structural difference is an allyl group on naloxone against a cyclopropylmethyl group on naltrexone, and the weights are 327.4 and 341.4.
Side by side
| Naloxone | Naltrexone | |
|---|---|---|
| Formula | C19H21NO4 | C20H23NO4 |
| Molecular weight | 327.4 g/mol | 341.4 g/mol |
| Family | Opioid antagonist | Opioid antagonist |
| Everyday group | OTC medicine | Prescription medicine |
| Functional groups | Alcohols, Aromatics, Ketones, Phenols, Ethers | Alcohols, Aromatics, Ketones, Phenols, Ethers |
| GHS signal wordThe supplier-filed hazard label, not a statement about ordinary use. | Danger | Danger |
| LD50A single acute animal measure. It ranks nothing about human safety. | 90 mg/kg (iv, mouse) | 1,450 mg/kg (oral, rat) |
| CAS number | 465-65-6 | 16590-41-3 |
| PubChem CID | 5284596 | 5360515 |
Structural similarity 0.75 of 1, computed as a Morgan fingerprint Tanimoto coefficient. It measures shape, not effect.
Common questions
- What is the difference between Naloxone and Naltrexone?
- These two are constantly confused, they differ by one small chemical group, and what they are used for could hardly be less alike. Both are opioid antagonists: they occupy the mu-opioid receptor and switch nothing on, which displaces any opioid already there. Naloxone is poorly absorbed by mouth and acts within minutes when injected or sprayed into the nose, which is why it is the overdose reversal agent carried in emergency kits.
- Is Naloxone bigger than Naltrexone?
- Naltrexone is the heavier molecule, 341.4 g/mol against 327.4 g/mol for Naloxone. Naloxone is C19H21NO4 and Naltrexone is C20H23NO4.
Read the full records: Naloxone and Naltrexone.