The investigators propose a pharmacokinetic pilot investigation with within-subjects (crossover) design, comparing two doses (0.8 mg; 1.6 mg) of buccal naloxone hydrochloride solution to the licensed intramuscular (IM; 0.8 mg) and intravenous (IV; 0.8 mg) routes of injection. The investigators will invite four healthy (i.e., non-opioid using) male volunteers (n=4, not powered), each of whom will attend four experimental sessions at counterbalanced sequence. Each volunteer will receive naloxone hydrochloride doses of 0.8 mg IM, 0.8 mg IV, 0.8 mg buccal, and 1.6 mg buccal, with only one dose administered per session.