Does Vivitrol (naltrexone) block opioids, and how complete is the blockade?
Vivitrol is an extended-release form of naltrexone, an opioid antagonist. It binds to opioid receptors and blocks opioids from activating them, which can reduce or prevent the euphoric and pain-relieving effects of opioid drugs. [1]
Because it’s an antagonist (not an opioid), it doesn’t produce opioid effects on its own.
What happens if someone takes opioids after a Vivitrol injection?
If a person takes opioids while naltrexone from Vivitrol is active, the opioids are generally less likely to produce expected effects because the receptors are blocked. [1]
A related safety point: starting or taking opioids can lead to precipitated withdrawal in people who still have opioids on board when naltrexone is initiated (this risk is one reason clinicians check for opioid exposure before starting treatment). [1]
How long does Vivitrol keep blocking opioids?
Vivitrol is designed for long-lasting receptor blockade, with dosing every month (once every 4 weeks). The company’s prescribing information describes an extended-release product intended to maintain opioid blockade over that interval. [1]
Does Vivitrol block all opioids equally?
Vivitrol blocks opioid receptors, so it works across opioid types that act on those receptors (such as heroin and prescription opioids). The strength of any opioid effects can vary by dose and timing, but the mechanism is receptor blockade by naltrexone. [1]
What if someone tries to override the blockade with more opioids?
Using more opioids to “break through” naltrexone is dangerous. Since naltrexone is blocking receptors, people may take higher doses hoping for effect, which can still cause overdose risk if the blockade decreases or wears off, especially as drug levels fall. [1]
Why do some people still feel symptoms while on Vivitrol?
Naltrexone blocks opioid effects, but it doesn’t treat all causes of craving, withdrawal symptoms, or pain. People may still experience symptoms unrelated to opioid receptor activation, and the timing of the injection versus any recent opioid use can matter (including the risk of precipitated withdrawal when starting naltrexone). [1]
Sources
[1] https://www.drugs.com/cons/vivitrol.html