As marijuana becomes legalized in many states across the U.S., the incidence of use is rising as well.  People are using marijuana for medicinal purposes, but more research is needed to find out if the chemicals in marijuana–called cannabinoids—are safe and effective.
Researchers also want to know how safe marijuana is for people in different age groups and how effective the substance is for those with long-term (chronic) illnesses–such as multiple sclerosis and epilepsy). 

A recent study, published in the journal Neuroscience, looked at the effects of marijuana on pregnant women, adolescents and people with Alzheimer’s disease (AD).

Incidence of Marijuana Use

Marijuana is at the top of the list of illegal substance use in the U.S.   As legalization continues to spread throughout the country, it’s anticipated that its use will continue to rise.

A recent letter published by the Journal of the American Medical Association reported that marijuana among pregnant women has risen dramatically since 2009.  In fact, it is the most popular illicit substance used by women who are pregnant.

Another growing segment of the population that uses marijuana is adolescents.  According to VeryWellMind, marijuana use among teenagers is more prevalent than alcohol use today.

What Does the Research Say?

The recent study, released by the Society of Neuroscience discovered that marijuana has a beneficial effect, as well as an adverse effect on the brain, depending on several factors.  For example, teenagers were found to be more vulnerable to damaging effects to the brain—that are life-long—because the brain is still developing during adolescence. Teenagers were discovered to have a disruption in both learning and memory as a result of marijuana use.  Marijuana was also found to adversely affect normal communication between various regions of the brain, as well as interfering with key neurotransmitters in teens.  Neurotransmitters are chemicals in the brain that are needed for the normal transfer of nerve impulses in the brain.

Another group in the study, found to be at high risk of long-term damaging effects of marijuana was the developing fetus (during pregnancy). 

As far as benefits are concerned, marijuana was found to help alleviate some of the symptoms of Alzheimer’s disease—such as memory problems.

Research Findings

Here are a few of the specific conclusions from recent animal studies:

1. In studies of prenatal rats, THC—the psychoactive substance in marijuana—produced an adverse effect, making the animals more prone to stress in later life.

2. Prenatal rats that were exposed to a THC-like chemical, experienced impaired formation of neuron (brain cell) circuits.

3. Marijuana, given to adolescent rats, was found to disrupt protein development in the area of the brain responsible for decision making, and self-control.

4. Adolescent rats exposed to marijuana experienced an increase in activity in the brain, involved in addiction—increasing the risk of addiction to marijuana and other substances in teenagers.

5. Long-term cannabinoid use negatively impacted brain connectivity involved in memory and learning in adult mice.

6. Treatment with THC—the psychoactive compound in marijuana—improved memory and lowered the level of nerve cell loss in mice with Alzheimer’s disease.

According to Michael Taffe, PhD, of Scripps Research Institute, “Today’s findings lend a new understanding of the complex effects that cannabis has on the brain.  While it may have therapeutic potential in some situations, it is important to get a better understanding of the negative aspects as well, particularly for pregnant women, teens, and chronic users.”


Human studies will be needed in the future to back up the evidence gathered in the animal studies.  In the meantime, preliminary evidence points to the probability that long-term marijuana use—particularly for young people and pregnant women– may not be as benign as many people believe it is.  But, for seniors with Alzheimer’s disease, the benefits may outweigh the risks.

Medical Marijuana Reduces Alzheimer’s-like Symptoms in Mice


Science Daily


The Society of Neuroscience