Lactating monkeys chronically receiving 2 mg THC per kilogram body weight orally either two or five times weekly were given a small dose of radiolabelled THC mixed with the THC. During the 24-hr observation period, approximately 0.2% of the labelled THC appeared in the milk.
Modified according to: Chao FC, Green DE, Forrest IS, Kaplan JN, Winship-Ball A, Braude M. The passage of 14C-delta-9-tetrahydrocannabinol into the milk of lactating squirrel monkeys. Res Commun Chem Pathol Pharmacol (1976 Oct) 15(2):303-317

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MONKEYS, HUH.