Nalmefene (Opvee)
Street names: Opvee, Nalmefene nasal spray, Long-acting Narcan
⚡What it does
- Long-acting opioid antagonist — kicks opioids off receptors and blocks them for ~11 hours (naloxone lasts 60–90 minutes)
- No opioid effect of its own; it cannot get you high
- Carried by an increasing number of US first-responder agencies since its 2023 FDA approval
⚠Key risks
- Precipitates sudden, severe withdrawal in opioid-dependent people — vomiting and agitation while semi-sedated is an aspiration risk
- Because it outlasts most opioids, re-overdose is less likely than with naloxone — but the withdrawal it triggers can drive immediate re-use once it wears off
- Not a substitute for emergency care: anyone reversed still needs monitoring
✚Overdose signs
- This IS an overdose antidote — the danger signs belong to the person being reversed: gasping then violent vomiting, chest pain, extreme agitation
- If the person re-sedates (rare with nalmefene), call emergency services again
Category comparison — Opioids
| Substance | Class | Top risks | Street price |
|---|---|---|---|
| Nalmefene (Opvee) | Rx-only — not a controlled drug; not abusable | Precipitates sudden, severe withdrawal in opioid-dependent people — vomiting and agitation while semi-sedated is an aspiration risk; Because it outlasts most opioids, re-overdose is less likely than with naloxone — but the withdrawal it triggers can drive immediate re-use once it wears off | Not a street drug — dispensed to EMS/ERs and by prescription |
| Heroin | Schedule I | Extremely addictive — physical dependence in weeks; Overdose: breathing slows or stops | ~$10–$40 per bag |
| Fentanyl | Schedule II | Respiratory depression; Addiction in days | ~$20–$40 per counterfeit pill |
| Fentanyl HCl (powder) | Schedule II / analogue prosecutions | Lab-purity powder is far stronger than street mixes; Weighing errors are fatal | ~$60–$120/gram wholesale equivalent |
| Acetylfentanyl | Schedule I | ~5–15× weaker than fentanyl but still deadly at gram-level mistakes; Frequent cause of cluster overdoses | ~$25–$60/g where found |
| Furanylfentanyl (Fu-F) | Schedule I | Linked to hundreds of fatal overdoses 2016–2018; Potency similar to fentanyl | ~$20–$50/g |
RxBrand names on the grey market
These brands are sold as this compound. Same molecule, different label and supply chain — quality varies enormously between them.
?Frequently asked questions
What does Nalmefene (Opvee) look like?
5 mg/0.5 mL single-dose nasal spray (bright blue device); hospital injection
What are the signs of a Nalmefene (Opvee) overdose?
This IS an overdose antidote — the danger signs belong to the person being reversed: gasping then violent vomiting, chest pain, extreme agitation; If the person re-sedates (rare with nalmefene), call emergency services again Call emergency services immediately and give naloxone if available — it reverses opioid overdoses.
How addictive is it?
Precipitates sudden, severe withdrawal in opioid-dependent people — vomiting and agitation while semi-sedated is an aspiration risk Dependence can develop with regular use.