File Photo: Researchers unveiled the link between marijuana and the frequency of sexual intercourse in a study which was published in the Journal of Sexual Medicine. Picture: Supplied

London - Where there is smoke, there tends to be fire, say medical researchers who found frequent marijuana users have about 20 percent more sex than those who abstain.

Researchers at Stanford University School of Medicine in the US unveiled the link between marijuana and the frequency of sexual intercourse in a study which was published in the Journal of Sexual Medicine.

Researchers in California reached their conclusion after a retrospective analysis of data on 50000 Americans aged 25 to 45, compiled from 2002 to 2015 by the National Survey of Family Growth. The Centres for Disease Control and Prevention sponsored the survey.

Respondents were asked how many times they had heterosexual intercourse in the past four weeks and how frequently they had smoked marijuana over the past 12 months, Stanford researchers said.

Women who were daily pot users had sex an average of 7.1 times during the previous four weeks, compared with the 6 times reported by those who denied using marijuana in the past year. For men, the daily users reported 6.9 times, compared with 5.6 for non-users.

“In other words, pot users are having about 20 percent more sex than pot abstainers,” said the senior author of the study Dr Michael Eisenberg, who is an assistant professor of urology at Stanford University.

Given that the average couple has sex about once a week, Eisenberg said, the bottom line for partaking in a bong or blunt could add up to 20 more instances of sexual intercourse each year.

“I think if you asked a man or a woman, 20 more times to have sex over a year, that would seem like a lot,” Eisenberg said.

It used to be thought that couples mostly smoked after sex but Eisenberg said his findings showed the opposite was true for “all races, ages, education levels, income groups and religions, every health status, whether they were married or single and whether or not they had kids”.

Marijuana is legal for medical or recreational adult use in 29 American states and the District of Columbia, said spokesperson Morgan Fox of the Marijuana Policy Project.

A record percentage of Americans - 64 percent - believe adult use of the drug should be legal, according to a Gallup poll published this week.

Eisenberg cautioned the study should not be misinterpreted as having proven a causal link.

“It doesn’t say if you smoke more marijuana, you’ll have more sex,” he said.

Still, for many, research in the name of science might never be so much fun.