According to the Dailymed site, "Naltrexone is a potent antagonist with a prolonged pharmacologic effect (24 to 72 hours)." I don't know if that's based on dosage or what, but to me it means that if you miss a pill, as long as you took one the day before the receptors should still be mostly blocked. That's conjecture on my part; I'd be interested to know what Dr. Eskapa or another professional thinks.