National Toxicology Program

[Federal Register: September 4, 1997 (Volume 62, Number 171)]
[Notices]
[Page 46751]

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DEPARTMENT OF HEALTH AND HUMAN SERVICES

Public Health Service

National Toxicology Program; Availability of Technical Report on Toxicology and Carcinogenesis Studies of 1-Trans-Delta⁹- Tetrahydrocannabinol

The HHS' National Toxicology Program announces the availability of the NTP Technical Report on the toxicology and carcinogenesis studies of 1-trans-delta⁹-tetrahydrocannabinol which is a major psychoactive component of marijuana and a widely used Schedule I substance.

Toxicology and carcinogenicity studies were conducted by administering 1-trans-delta⁹-tetrahydrocannabinol (THC) in corn oil to groups of 62 vehicle control male rats, 60 low-dose male rats, 70 mid- and high-dose male rats, and 60 female rats at doses of 0, 12.5, 25, or 50 mg THC/kg body weight by gavage for 104 to 105 weeks. Groups of 62 vehicle control male mice, 60 low-dose male mice, 61 mid-dose male mice, and 60 high-dose male mice and 60 female mice were administered 0, 125, 250, or 500 mg THC/kg body weight in corn oil by gavage for 104 to 105 weeks (males) or 105 to 106 weeks (females).

Under the conditions of these 2-year gavage studies, there was no evidence of carcinogenic activity* of 1-trans-delta⁹- tetrahydrocannabinol in male or female F344/N rats administered 12.5, 25, or 50 mg/kg. There was equivocal evidence of carcinogenic activity of THC in male and female B6C3F1 mice based on the increased incidences of thyroid gland follicular cell adenomas in 125 mg/kg groups.

Increased incidences of thyroid gland follicular cell hyperplasia occurred in male and female mice, and increased incidences of hyperplasia and ulcers of the forestomach were observed in male mice.

The incidences of mammary gland fibroadenomas and uterine stromal polyps were decreased in dosed groups of female rats, as were the incidences of pancreatic adenomas, pituitary gland adenomas, and interstitial cell adenomas of the testis in dosed male rats and liver neoplasms in dosed mice. These decreases were likely related to lower body weights in dosed animals.

Questions or comments about the Technical Report should be directed to Central Data Management at PO Box 12233, Research Triangle Park, NC 27709 or telephone (919) 541-3419.

Copies of Toxicology and Carcinogenesis Studies of 1-Trans- Delta⁹-Tetrahydrocannabinol (CAS No. 1972-08-3) (TR-446) are available from Central Data Management, NIEHS, MD E1-02, PO Box 12233, Research Triangle Park, NC 27709; telephone (919) 541-3419.

Dated: August 14, 1997

_______________________________
Samuel H. Wilson,
NIEHS Deputy Director

[BILLING CODE 4140-01-M]

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*The NTP uses five categories of evidence of carcinogenic activity observed in each animal study: two categories for positive results ("clear evidence" and "some evidence"), one category for uncertain findings ("equivocal evidence"), one category for no observable effect ("no evidence"), and one category for studies that cannot be evaluated because of major flaws ("inadequate study").