STUDY LINKS USE OF MARIJUANA TO A FLUCTUATION IN SEX DRIVE
Pharmacological researchers may have resolved the contradiction between scientific findings that marijuana decreases sexual drive and reports from users who maintain the drug works as an aphrodisiac.
In the journal Science three researchers from the University of Texas suggest that tetrahydrocannabinol, or THC, marijuana's active ingredient, may affect male sexual activity in two phases. In animal tests, they found, it first raises the level of testosterone and other sex hormones but later may lower hormone levels to far below normal.
Previous laboratory studies failed to detect the initial rise in hormone levels because scientists usually do not begin measuring those levels until at least one hour after the drug is administered, said Susan Dalterio, assistant professor of pharmacology, obstetrics and gynecology at the University of Texas Health Center in San Antonio.
''One thing that bothered those of us who do animal work was that every time we gave THC to mice, they would show a decrease in sexual behavior,'' Dr. Dalterio said in a telephone interview. ''But then human beings who smoke marijuana would tell us, 'Hey, you're crazy! It increases our sex drive.' '' Hormone Levels Measured
In their current study, the researchers measured levels of blood testosterone and luteinizing hormone, or LH, which stimulates testosterone production, within the first hour after feeding liquid THC to mice.
They found that the testosterone level in all the mice jumped almost immediately to about six times its normal amount. Moreover, mice receiving low doses of the drug maintained the high testosterone levels for the entire hour; those receiving much higher doses showed drastic drops in testosterone after 20 minutes to levels considerably below those of mice in the control group.
In a person smoking marijuana, the THC enters the bloodstream very rapidly, Dr. Dalterio said. The drug's almost instant effect on the testes, as shown in the study, would seem to account for the dramatic reports of sexual arousal during and after smoking, she said.
The results also seem to explain previous reports of depleted testosterone levels among heavy marijuana users, according to Dr. Dalterio. In the study doses of THC that were 10 to 100 times higher than the low doses caused a simultaneous rise in luteinizing hormone, which is manufactured in the pituitary gland at the brain's base. Normal Controls Disrupted
In normal sexual stimulation, Dr. Dalterio explained, it takes about 20 minutes for LH to be produced, then travel from the pituitary to the testes, where it helps produce testosterone; in about the same amount of time the testosterone then enters the bloodstream and makes the trip back to the pituitary. This feedback system automatically shuts down when the brain senses an adequate level of sex hormone has been reached.
Heavy doses of THC disrupt the normal flow in this hormonal loop by triggering LH and testosterone production at the same time, she said. This appears to cause a shutdown that sends hormonal levels plummeting 20 minutes after the drug is administered. No such testosterone drop was seen among mice that received low doses.
If the same processes occurs in humans, the report says, ''the anecdotal reports on the aphrodisiac effects of marijuana and the evidence for suppression of testicular activity after heavy use of this substance are not contradictory.''
STUDY LINKS USE OF MARIJUANA TO A FLUCTUATION IN SEX DRIVE - The New York Times
