This invention relates to cocrystals of naloxone and of naltrexone and their use as opioid antagonists. The cocrystals of the invention include naloxone isonicotinamide cocrystal, naloxone hydrochloride piperazine cocrystal, naltrexone menthol cocrystal, naltrexone thymine cocrystal, naltrexone 2,5-dihydroxybenzoic acid cocrystal, naltrexone salicylic acid cocrystal, naltrexone hydrochloride piperazine cocrystal and naltrexone hydrochloride sulfathiazole cocrystal. A drug-in¬ adhesive transdermal patch containing the opioid analgesic fentanyl or an analog thereof and a cocrystal of naloxone or naltrexone is disclosed. Also disclosed is a method of treating pain, such as acute, chronic or intermittent pain, by applying a drug-in-adhesive transdermal patch of the invention to the skin of a patient in need thereof. Also disclosed is an improved transdermal patch for administering fentanyl or an analog thereof, or for administering a mu opioid agonist, the improvement wherein the transdermal patch contains a cocrystal of the invention in an abuse limiting amount. The improved transdermal patch may be a drug-in-adhesive transdermal patch or a reservoir transdermal patch.
