Marijuana is well known to bring upon the "munchies" or, a temporary increase in appetite, yet its effect on weight gain is more complex than it seems, according to a new study.

"As to whether it actually causes weight gain in the long term, the available data is limited," says Didier Jutras-Aswad of the University of Montreal. "The question is all the more difficult to answer since many other factors can influence weight."

Those who smoke cannabis, says Jutras-Aswad, might also smoke cigarettes, which is well known to suppress the appetite.

Furthermore, marijuana affects users differently depending on their gender and how much they use it.

The research team concluded that long-term cannabis use leads to weight gain, however, this effect is vulnerable to gender and concomitant cigarette smoking, says Jutras-Aswad.

Beginning at age 12, 1,294 young participants revealed their diet, overall mental and physical health -- which included increases in height and weight -- exercise habits and their use of substance including nicotine, alcohol and cannabis.

The wealth of information on their subjects allowed researchers to rule out factors that could be mistaken as culprits of weight gain.

"The effects of these substances observed in highly controlled laboratory settings are more complex than anticipated in real-world settings," says Jutras-Aswad.

They concluded that marijuana led to weight gain in males who don't use cigarettes, but for those who did, the effect was nearly the opposite.

At press time, the research team is unable to explain marijuana's effect on males versus females, although they offer hypotheses about Tetrahydrocannabinol (THC), its active ingredient.

"THC and nicotine do not affect the neurobiological circuits controlling hunger in the same way in men and women," says Jutras-Aswad. "We also know that these targets in the brain are modified by hormonal factors that can fluctuate, in particular, during menstrual cycles."

He cites psychological differences, suggesting that women are more likely to worry about weight gain and restrict their diets to make up for those nights when they had the munchies.

The study was published in the journal Pharmacology Biochemistry and Behavior.