SHEET /vs/morphine-vs-fentanyl · COMPARISON
Morphine vs Fentanyl: what is the difference?
How they differ
Both bind the same target, the mu-opioid receptor, and the enormous difference between them is how tightly and how easily they get there. Morphine is the natural alkaloid isolated from opium poppy in 1804, a rigid five-ring structure with two hydroxyl groups that make it relatively water-loving and slow to cross into the brain. Fentanyl is fully synthetic, much smaller in ring count, and far more fat-soluble, so it reaches the brain in minutes and acts at a small fraction of the amount. The reported oral LD50 values sit at 335 mg/kg in rats for morphine and 18 mg/kg in rats for fentanyl, a ratio that understates the difference in potency at ordinary exposures. That potency gap is the reason fentanyl dominates overdose statistics: the margin between a working amount and a fatal one is measured in units a kitchen scale cannot see.
Side by side
| Morphine | Fentanyl | |
|---|---|---|
| Formula | C17H19NO3 | C22H28N2O |
| Molecular weight | 285.34 g/mol | 336.5 g/mol |
| Family | Opioids, Non-opioid painkillers | Opioids |
| Everyday group | Prescription medicine | Prescription medicine |
| Functional groups | Alcohols, Aromatics, Phenols, Ethers | Aromatics, Amides |
| GHS signal wordThe supplier-filed hazard label, not a statement about ordinary use. | Warning | Danger |
| Oral LD50A single acute animal measure. It ranks nothing about human safety. | 335 mg/kg (oral, rat) | 18 mg/kg (oral, rat) |
| CAS number | 57-27-2 | 437-38-7 |
| PubChem CID | 5288826 | 3345 |
Common questions
- What is the difference between Morphine and Fentanyl?
- Both bind the same target, the mu-opioid receptor, and the enormous difference between them is how tightly and how easily they get there. Morphine is the natural alkaloid isolated from opium poppy in 1804, a rigid five-ring structure with two hydroxyl groups that make it relatively water-loving and slow to cross into the brain. Fentanyl is fully synthetic, much smaller in ring count, and far more fat-soluble, so it reaches the brain in minutes and acts at a small fraction of the amount.
- Is Morphine bigger than Fentanyl?
- Fentanyl is the heavier molecule, 336.5 g/mol against 285.34 g/mol for Morphine. Morphine is C17H19NO3 and Fentanyl is C22H28N2O.
- Which has the lower reported LD50, Morphine or Fentanyl?
- Fentanyl, at 18 mg/kg (oral, rat), against 335 mg/kg (oral, rat) for Morphine. 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.