Women are more likely to suffer negative effects of smoking cannabis - including depression, anxiety and paranoia - because their oestrogen levels make them more sensitive to its active ingredient, according to new research.
U.S. researchers found that female rats were at least 30 per cent more sensitive than males to the pain-relieving qualities of tetrahydrocannabinol (THC), the active ingredient in cannabis, because of their increased oestrogen levels.
Experts said that the increased concentration of THC in today's cannabis meant smokers are more likely to experience negative effects including anxiety, confusion, panic attacks, hallucinations or extreme paranoia, with women more at risk than men.
Previous studies have shown that women are more prone to cannabis abuse and dependence than men.
In women, cannabis withdrawal symptoms including irritability, sleep disruption and decreased food intake were shown to be more severe.
Women were also more likely to relapse when trying to quit smoking the drug.
The only effect of THC which appears to be more pronounced in men is in terms of appetite.
Studies in California found that THC stimulated the appetites of male animals more than those of females, meaning the "munchie effect" might be stronger for men than women.
The new study, published in journal Drug and Alcohol Dependence, looked at the pain-relieving effects of THC on male and female rats.
After ten days of treatment, female rats were shown to be significantly more tolerant to THC than males.
Tolerance occurs when the rat "adapts" to THC so that larger doses are required to produce the same pain-relieving effects seen with the first dose.
Researchers expected females to be more sensitive to THC, so adjusted their doses to be 30 per cent lower than the doses for males. The females still developed more tolerance.
Lead author Professor Rebecca Craft, of Washington State University said: "This is the lowest dose anyone has ever used to induce tolerance.
"What we're finding with THC is that you get a very clear spike in drug sensitivity right when the females are ovulating - right when their oestrogen levels have peaked and are coming down," she said.
Professor Craft warned that marijuana that exists today has much higher concentrations of THC than in previous years, meaning negative side effects are much more likely, with women at higher risk due to their increased sensitivity to the compound.
"Marijuana is very different than it was 40 years ago," she said. "It's much higher in THC and lower in cannabidiol, so a little bit goes a very long way.
"We're more likely to see negative side effects today like anxiety, confusion, panic attacks, hallucinations or extreme paranoia. And women are at higher risk."
She added that despite the known differences in how marijuana affects women and men, most THC tolerance studies have been done on males as women's hormone levels tend to vary throughout the month.
Researchers also found that a low dose of THC did not disrupt the reproductive cycle in female rats, which has been under debate.
- Daily Mail