Frequent marijuana smokers are not known for their stamina and, according to a recent study at Buffalo University, neither are their sperm.

Though experts have said for years that heavy marijuana use has negative effects on fertility, the BU study is the first to discover exactly why.

Scientists at Buffalo University found that regular smokers had significantly less seminal fluid and a lower sperm count. Their sperm were also more likely to swim too fast, too early, leading to burnout before they reach the egg.

“The bottom line is the active ingredients in marijuana are doing something to sperm,” Dr. Lani Burkman, the study’s lead researcher, said.

Just what that “something” is has yet to be proven, but the researchers believe that the THC (tetrahydrocannabinol) in marijuana may disrupt the way sperm swim, or it may block mechanisms designed to weed out malfunctioning sperm.

“In research studies, men who were heavy users of marijuana had lower testosterone levels and decreased sperm counts,” Dr. Marjorie Greenfield, a renowned pregnancy expert, said. “But you certainly couldn’t rely on a low sperm count as a birth-control method if you didn’t want to get pregnant.”

It is known that human sperm contains receptors that are stimulated by substances like THC and other cannabis-related chemicals, and previous tests have shown that sperm exposed to high levels of THC swim in an abnormal fashion. This abnormal swimming pattern then decreases the sperm’s chances of attaching to the egg and therefore reduces the chances of fertilization.

In the current study Dr. Burkman’s team carried out a series of tests on sperm samples taken from 22 men who had smoked marijuana on average 14 times a week for at least five years. The scientists paid particular attention to when the subjects’ sperm began to swim in an abnormal fashion. Their results found that the test subjects’ sperm were swimming too fast, too early.

Just as a marathon runner must keep a steady pace in order to complete the entire run, sperm must maintain a pace that will allow them to complete their journey to the egg.

In the marijuana users’ tests, the sperm began swimming very fast as soon as they were released, and a majority of sperm never made it to the egg.

“The timing was all wrong. These sperm will experience burnout before they reach the egg and would not be capable of fertilization,” Burkman said.

In order for a sperm to fertilize an egg, the sperm must be able to swim very fast at the end of the journey, and since marijuana screws up the pace of users’ sperm, the chances of fertilization were greatly decreased.

“Many female partners of men with low sperm counts will eventually conceive — it may just take longer,” Dr. Greenfield said.

The study’s results were not troubling to University of Wisconsin senior Carl Swanson. When asked if he was concerned about his marijuana use affecting future fertility, Swanson replied, “It does? Seriously? Sweet!”

“That actually sounds like something beneficial,” Swanson continued. “I’m definitely not interested in getting anyone pregnant any time soon, so I don’t really think it’s a big deal.”

A UW junior, who wishes to be identified as Mike W., agrees.

“At this point in my life, it doesn’t really bother me,” Mike W. said. “If I was still doing it when I was married, I could probably give it up for a while, you know?”