Opioid antagonist: How they work and when to use them
Want a clear, no-nonsense explanation of opioid antagonists? These drugs block or reverse the effects of opioids. That makes them lifesavers in an overdose and useful in treating dependence. Two names you’ll hear most are naloxone and naltrexone — they look similar in name but work in different situations.
How opioid antagonists work
Opioids attach to brain receptors and cause pain relief, drowsiness, and slowed breathing. An opioid antagonist fits those same receptors but doesn’t activate them. Instead it kicks opioids off the receptor, reversing their effects. Naloxone acts fast and is used for sudden overdoses — think emergency fix. Naltrexone lasts much longer and helps prevent opioid effects over days or weeks, which is why doctors use it for ongoing treatment of dependence.
Naloxone works within minutes after a nasal spray or injection. If someone’s breathing is slow or they’re unresponsive, naloxone can restore breathing and wake them up enough for medical help to arrive. Naltrexone needs someone to be opioid-free first; taking it while still using opioids can trigger withdrawal. So naltrexone is a maintenance tool, not an emergency one.
Practical tips: getting and using these medications
In Canada, naloxone kits are widely available at many pharmacies and community programs without a prescription. Look for nasal sprays (often labeled as naloxone or brand names like Narcan) — they’re simple to use. Learn how to spot an overdose: very slow or no breathing, unresponsive, blue lips or face. If you suspect overdose, call emergency services, give naloxone if available, and do rescue breathing if trained.
For people managing opioid dependence, talk to a healthcare provider about naltrexone options. There’s an oral pill and an extended-release injection that lasts about a month. Before starting naltrexone you must be off opioids for a period set by your clinician to avoid sudden withdrawal. Your provider can explain timing, dosing, and follow-up care.
Side effects? Naloxone is generally safe and short-acting; it can cause sudden withdrawal symptoms in people physically dependent on opioids — nausea, sweating, agitation. Naltrexone can cause nausea, liver enzyme changes, or headaches. Always tell your provider about other medications and medical conditions, especially liver problems.
Want to be prepared? Carry naloxone if you or someone you know uses opioids, even occasionally. Learn how to use the kit, store it at room temperature, and replace it before the expiry date. If you’re helping someone through recovery, ask your clinic about naltrexone as one tool among counselling, support groups, and other medical treatments.
Browse our posts tagged “opioid antagonist” for practical articles on naloxone access, treatment options, and safe buying tips. If you need immediate help for an overdose, call emergency services right away — naloxone helps, but professional care matters.
