Despite a shortage of research on the topic, it's been suggested that drugs affect men and women differently. And because of the recent legalization of recreational marijuana in Colorado and Washington and medical marijuana in 23 states, it's now more important than ever that women understand how THC affects their body chemistry specifically.
Researchers at Washington State University have found evidence indicating that females may build up a tolerance to marijuana more easily than males do.
"It's not entirely predictive, but if you become rapidly tolerant to a drug, you may be at greater risk for developing an addiction," Professor Rebecca Craft, chair of the psychology department at WSU and lead researcher of the study, told HuffPost. (She also noted that tolerance by itself does not define drug dependence and that tolerance is only one characteristic of addiction.)
Translation: Women may want to think twice before matching a man joint for joint.
The study focused on the pain-relieving effects of THC on male and female rats. In this case, rats made for good subjects, because, like humans, rats have a menstrual cycle (albeit one that lasts four to five days instead of 28), and they experience similar ovarian hormone fluctuations, which affect pain.
At the beginning of the trial, the female rats displayed a higher sensitivity to THC than the males. However, after 10 days of testing, researchers found that the female rats were needing higher doses of THC than the males just to experience the same degree of pain relief. In other words, while female rats started out being more sensitive to THC, after 10 days, they ended up less sensitive.
"We were looking at the pain-relieving effects," Craft said. "One of the things that is of concern if you're using any medication repeatedly is: Will it maintain its effectiveness over time?"
There have been a number of clinical trials in humans suggesting that marijuana and cannabinoid drugs alleviate pain. For women, this is an important issue, since medical researchers are now seriously considering these drugs' potential to relieve chronic pain -- something women in particular will benefit from if administered properly.
"Over their lifetime, women actually suffer quite a bit more pain than men do," Craft said. "So women have a lot of need for analgesic drugs."
As of now, rats are the most convenient method of exploring possible gender disparities in the pain-relieving effects of drugs, given their aforementioned hormone similarities to humans, as well as the difficulty of wrangling busy human test subjects to come into the lab at frequent, hyper-specific points of their cycles.
Craft is confident that these results are generalizable to humans, but she said that you can never be sure until you actually begin testing people.
"There are some differences in the species in terms of how they metabolize drugs," Craft said. "You really want to see some kind of confirmation that the same thing is happening in humans."
In a 2014 study, women reported feeling the "high" sensation more acutely than men when given a joint to smoke. This sensitivity, combined with Craft's findings, can better inform doctors who want to prescribe cannabis as a pain reliever and women who smoke cannabis recreationally.
Craft noted that it's possible today to get much stronger marijuana than when the drug first rose to popularity in the 1960s and '70s, and that it's easier now than ever to observe potential differences in how men and women respond to the drug. She suggested that women educate themselves about marijuana use and proceed with caution, just as they would with liquor consumption.
Marijuana addiction does occur, though only in a small percentage of cases.
"I think it's great that there's been a social change in the fact that recreational drug use is more acceptable now than it used to be," said Craft. "But there are some greater risks for women with some drugs, and I think they need to be aware of that."
This article has been updated with quotes from Craft, as well as additional information, regarding the correlation between tolerance and risk for addiction.