Cannabis is the most widely used illicit drug with more than 181 million consumers worldwide. It is often considered to be primarily a male problem: men make up three quarters of users, consume larger quantities, and are twice as likely to become dependent. Fewer women use cannabis, do so in smaller amounts, and start smoking later than men.
Studies have identified differences in male and female cannabis users that could inform how we treat cannabis addiction for individual users. But the evidence may not be adequate.
First it’s important to note when discussing differences between large groups within society, such as sex differences, these are seen at the population level when we average across these two groups. There will be many individual men and women who do not fall into these categories.
Men and women generally have different motivations for using cannabis. Men, on average, are more strongly influenced by external factors, such as cannabis availability and peer use. Men also tend to have a strong cannabis-using social network.
Among cannabis users who seek treatment, men consume higher quantities of alcohol and tobacco and have more criminal convictions and personality disorders.
Women are less likely to seek treatment, often because they fear losing custody of their children, because of difficulties in finding assistance for childcare and due to the lack of services for pregnant women.
Chemicals in cannabis exert their effects by binding to particular receptors in the brain. Sex hormones affect the density and function of these receptors, causing sex differences in the way cannabis affects the brain.
In animal studies, large doses of cannabis over long periods caused long-lasting effects on emotion: male rats exhibited reduced motivation, while female rats showed depressive-like behaviours. Chronic cannabis administration altered brain areas controlling motivation in female rats and in areas involved in stress and memory in males.
Unfortunately, we know little about whether cannabis affects cognition differently in men and women. Some studies show that chronic use is associated with lower memory in women; and poorer decision-making and reaction time in men; others show no sex effects.
Few studies have examined if cannabis affects the brain differently in men and women. Neuroimaging studies are expensive and involve small numbers of participants. Almost half of the studies have focused almost exclusively on men to minimise any differences between individuals that may undermine our certainty of the results, to the detriment of women who may respond to cannabis differently.
The inconsistent evidence, the potential for false positives and publication bias (where studies showing positive results are more likely to be published), prevent scientists from drawing firm conclusions about how sex affects the way the brain processes cannabis.
When comparing men and women, it is difficult (if not impossible), to examine the pure effects of biological sex and gender (cultural and social factors associated with biological sex).
Animal studies are conducted in highly controlled environments that allow scientists to investigate sex effects, but are limited in their ability to tell us about human sex differences. In humans, we cannot fully disentangle sex from gender effects, as sex is systematically linked to many other psychological, social and cultural factors.
Men and women show different reasons for using cannabis, patterns of use and harms experienced. Unfortunately, we know very little about the role of sex on how cannabis affects the human brain and cognition, if at all.
Valentina Lorenzetti, Postdoctoral Research Fellow of the Brain & Mental Health Laboratory, Monash Institute of Cognitive and Clinical Neurosciences, MONASH University, Monash University and Adrian Carter, Senior Research Fellow, Monash University