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3235705 
Journal Article 
Interaction between naltrexone and oral THC in heavy marijuana smokers 
Haney, M; Bisaga, A; Foltin, RW 
2003 
1 
Psychopharmacology
ISSN: 0033-3158
EISSN: 1432-2072 
166 
1 
77-85 
WOS:000181536000009 
Rationale: Studies in non-human animals suggest that opioid
antagonists block the reinforcing effects of cannabinoids. Objective: The present studies in
humans investigated how naltrexone modulates (1) the subjective and physiological effects of oral
THC in comparison to methadone, (2) the reinforcing effects of oral THC, and (3) plasma levels of
oral THC. Methods: In study 1, marijuana smokers (n=9) received naltrexone (0, 50 mg) followed 30
min later by THC (0, 15, 30 mg) or methadone (5, 10 mg). Subjective effects, task performance,
pupillary diameter, and cardiovascular parameters were measured repeatedly. In study 2a,
marijuana smokers (n=23) were randomly assigned to one THC dose condition (0, 15 or 30 mg). One
set of color-coded capsules containing THC and active naltrexone (50 mg) was given in one
session, while another set of color-coded capsules containing THC and placebo naltrexone was
given in another session. In the final three sessions, participants chose which color capsules
they would receive. In study 2b, a subset of participants from study 2a (n=7) received naltrexone
(0, 50 mg) 30 min prior to oral THC (30 mg) administration, and blood was drawn repeatedly.
Results: Pretreatment with naltrexone significantly increased many of the ""positive"" subjective
effects of oral THC (30 mg) e.g. ratings of Good Drug Effect and Capsule Liking. Naltrexone
tended to increase the reinforcing effects of oral THC (30 mg), as indicated by performance in a
drug choice test. Naltrexone did not alter plasma THC levels. Conclusions: These studies
demonstrate that naltrexone increases the subjective effects of oral THC. Thus, oral THC's
effects are enhanced rather than antagonized by opioid receptor blockade in heavy marijuana
smokers. 
opioid; cannabinoid; marijuana; choice; methadone