Does cannabis use during pregnancy affect all children in the same way? This study suggests it doesn’t. Researchers worked with mice that were selectively bred to have different “personalities”: some were naturally dominant and more resilient to stress, while others were more submissive and sensitive.

When pregnant mice were exposed to THC (the main psychoactive component in cannabis), the effects on their offspring varied dramatically. The dominant, stress-resilient mice—who would normally cope well with challenges—actually showed increased anxiety as adults. In contrast, the more sensitive mice showed the opposite pattern: they became more social and displayed lower levels of anxiety.

Beyond behavior, the researchers also observed changes in the brain. They found differences in gene activity related to the endocannabinoid system (which helps regulate mood, stress, and emotional balance) and the dopamine system (linked to motivation and reward). These biological shifts may help explain why the same exposure leads to very different outcomes.

Another important finding was that these effects appeared early in life and could persist over time, suggesting that prenatal exposure may have long-lasting impacts on development.

The key takeaway is that there isn’t a single, predictable response to cannabis exposure during pregnancy. Instead, its effects seem to depend on underlying temperament and brain biology. This highlights how complex and individualized the impact of prenatal cannabis exposure can be—and why it’s difficult to assume it is either entirely safe or uniformly harmful.