A study released today underlines both the dangers and the therapeutic potential of cannabis, revealing different effects across the lifespan. Cannabis exposure in the womb or during adolescence may disturb learning and memory, damage communication between brain regions, and distract levels of key neurotransmitters and metabolites in the brain.

In Alzheimer’s, however, substances found in marijuana, such as THC, may improve memory and alleviate some of the disease’s symptoms. The findings were presented at Neuroscience 2018, the annual conference of the Society for Neuroscience and the world’s largest source of emerging news about brain science and health.

Cannabis is the most frequently used illicit drug in the United States and its popularity is expected to increase as it is legalized in more places. It is also the illegal drug most commonly used by pregnant women, in spite of the potential for long-term harm to the fetus. Many people start using cannabis as teenagers — a predominantly vulnerable time as the brain is still developing — when there is sign for amplified risk. At the same time, a growing number of people are turning to cannabis for the relief of symptoms of chronic diseases such as epilepsy and multiple sclerosis. These use patterns show the need to better comprehend the long-term effects of cannabis, particularly in sensitive populations such as unborn children and adolescents.

The new conclusions show that: prenatal exposure to THC in rats makes the animal more vulnerable to stress later in life; Rats exposed to synthetic compounds similar to THC impaired formation of the neural circuits involved in learning and memory as adolescents; Cannabinoid use by adolescent rats boosts activity in brain paths responsible for habit formation; In adolescent rats, cannabinoids may disturb the development of a protein lattice important for balancing excitatory and inhibitory activity in a brain region involved in decision-making, planning, and self-control; Long-term cannabinoid use alters metabolism and connectivity of brain regions involved in learning and memory in adult mice; Treating Alzheimer’s disease mice with the psychoactive compound found in marijuana improves memory and reduces neuronal loss, suggesting a possible therapy for the human disease.