“THC has an antagonistic effect against histamine on the isolated perfused guinea-pig lung and rabbit kidney. This antagonism seems to be a competitive one at the concentrations used and interacts with histamine at H1-receptors. THC also antagonizes the effect of acetylcholine, PGE2, angiotensis II and histamine in the isolated continuously superfused guinea-pig ileum by a non-competitive manner. The antagonism between THC and histamine on the isolated superfused rabbit aortic strips was found to be highly specific, since 100% relaxation was obtained when the muscle contracted by histamine but not by the equipotent doses of angiotensin II and noradrenaline. THC also causes a significant increase in survival time of guinea-pigs when the animals were exposed to histamine aerosol. These results indicate a specific antagonism of THC against histamine in the preparations used in this investigation.”

http://www.ncbi.nlm.nih.gov/pubmed/239651

“antihistaminic /an·ti·his·ta·min·ic/ (-his-tah-min´ik)