SAN ANTONIO (Reuters Health) - A new study shows that men who smoke marijuana frequently have significantly less seminal fluid, a lower total sperm count and abnormally behaving sperm.

"The bottom line is, the active ingredients in marijuana are doing something to sperm, and the numbers are in the direction toward infertility," said lead study author Lani Burkman, Ph.D., who is an assistant professor of gynecology & obstetrics at the State University of New York at Buffalo.

Burkman today presented her study here at the annual meeting of the American Society for Reproductive Medicine. She said it is the first study to assess marijuana's effect on specific swimming behavior of sperm from marijuana smokers and to compare the results with sperm from men with confirmed fertility.

While marijuana also contains other cannabinoids, Burkman said it is tetrahydrocannabinol (THC) that appears to be harming male fertility. "THC may be causing improper timing of sperm function by direct stimulation, or it may be bypassing natural inhibition mechanisms. Whatever the cause, the sperm are swimming too fast too early," explained Burkman. She said this aberrant pattern has been connected to infertility in other studies.

In the current study, the researchers received seminal fluid from 22 confirmed marijuana smokers and subjected the samples to a variety of tests. The volunteers reported smoking marijuana approximately 14 times a week for an average of 5.1 years.

The sperm from the pot smokers was compared to sperm obtained from 59 fertile men who had produced a pregnancy. All men abstained from sexual activity for two days before the lab analysis.

The samples from both groups were tested for volume, sperm-count-per-unit of seminal fluid, total sperm count, percent of sperm that was moving, velocity and sperm shape. In addition, sperm were assessed for hyperactivation, a closely regulated and very vigorous type of swimming that is required as the sperm approaches the egg. Burkman and her colleagues evaluated hyperactivation and velocity while the sperm was in seminal fluid and again after washing and incubation, when the dead sperm were eliminated.

The researchers found the volume of seminal fluid and the total number of sperm from marijuana smokers were significantly less than for fertile control men. Significant differences also appeared when hyperactivation and velocity (before and after washing) were assessed.

"The sperm from marijuana smokers were moving too fast too early," said Burkman. "The timing was all wrong. These sperm will experience burnout before they reach the egg and would not be capable of fertilization."

She said while men who smoke pot have fathered children, her study shows that chronic marijuana smoking may leave a male with only borderline fertility potential. Burkman said a man would need to abstain from pot smoking for a period of 4 months or longer, at least theoretically, before their fertility potential could return to normal.

"If you are smoking a lot of marijuana you are messing up a normal system that is operating in your body," said Burkman in an interview with Reuters Health. "We would advise current smokers of marijuana that they need to get off of it for several months. The reason is that THC is stored in their fat and it will take months to come out of their fat."

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