In teenagers transitioning from adolescence to early adulthood, heightened risks for marijuana addiction appear to be linked to widespread, marijuana-related changes in brain development, a team of researchers from two U.S. institutions reports.
Teenage consumers of marijuana/cannabis are substantially more likely to develop diagnosable cases of marijuana addiction than their adult counterparts. Doctors and researchers don’t fully understand the underlying reasons for this fact. However, in a study published in January 2015 in the journal Drug and Alcohol Dependence, researchers from Harvard Medical School and Mount Sinai Hospital used laboratory experiments on rats to explore the impact that marijuana use has on the developing brains of teenagers. These researchers concluded that elevated teen addiction risks stem at least partially from changes that marijuana’s main ingredient, THC, introduces into the normal development process.
When consumed in any substantial amount, THC (tetrahydrocannabinol) produces an increase in the levels of a key chemical, called dopamine, found in the brain’s pleasure center. In turn, elevated dopamine levels in the pleasure center lead to the onset of an unusually pleasurable sensation called euphoria. While THC also has a number of other effects on brain function, it is the boost in euphoria levels that largely explains the drug’s ability to trigger addiction. This is true because a person who repeatedly uses marijuana gradually changes the way in which his or her pleasure center handles its dopamine supply.
Eventually, persistent changes in dopamine production and processing can lead to a physical dependence on continued intake of the drug. In turn, a physical dependence on marijuana can easily form the basis for an uncontrolled cannabis addiction.
Signs Of Marijuana Addiction
Specific indicators of marijuana/cannabis addiction include:
- a repeatedly demonstrated inability to limit consumption
- the onset of marijuana/cannabis cravings between periods of active use
- rising tolerance to the mind-altering effects of any given quantity
- the development of withdrawal symptoms when the brain goes too long without receiving its expected dose
Along with other symptoms indicating the presence of non-addicted marijuana abuse, these symptoms form the criteria for the diagnosis of a mental health condition called cannabis use disorder.
Marijuana’s Impact On Teenagers
Teenagers who regularly consume even small quantities of marijuana have higher chances of developing an addiction than their adult counterparts. While about 9 percent of users in general will someday meet the criteria for diagnosing marijuana/cannabis addiction, fully 17 percent of teen users will someday meet these criteria, according to data compiled by the National Institute on Drug Abuse.
Brain Effects Of THC
Short-term brain effects of THC use in adolescents and adults include:
- an impaired ability to learn new things
- an impaired ability to make new memories or recall previously formed memories
- a reduced ability to think critically
- a reduced ability to make sound judgments
- a reduced ability to maintain proper muscle coordination or body balance
In addition, people who start consuming marijuana as teenagers may shave roughly eight points from their adult IQ scores (and may never recover these lost points, even after suspending intake of the drug).
THC And Brain Development
In the study published in Drug and Alcohol Dependence, researchers used extensive experiments on two groups of rats to assess the impact that THC use has on aspects of teen brain development, such as the normal growth of blood vessels and the normal function of the genes responsible for making and transporting dopamine. One group of rats received regular doses of THC for a set amount of time and had their brain functions and structures examined while still in adolescence. The other group of rats received regular doses of THC for the same amount of time and had their brain functions and structures examined after reaching adulthood.
The researchers concluded that the presence of THC in the rats’ brains significantly altered several key aspects of the course of normal growth and development in adolescence. They also concluded that the worst effects of THC use appeared in the transitional period between adolescence and adulthood, when the animals had actually stopped consuming the substance. Some of the observed changes in dopamine-related function occurred in multiple brain areas.
The study’s authors concluded that dopamine-related changes and other brain function changes triggered by the effects of THC help make teenagers more susceptible to developing marijuana addiction, in addition to making them more likely to experience such problems as marijuana-induced psychosis (delusions and/or hallucinations) and a reduced IQ in adulthood.
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