Recently, the World Health Organization published a report titled “The health and social effects of non-medical cannabis use”—the first in the last twenty years. The extensive research did not consider the toxicology, pharmacology, or possible medicinal applications of marijuana but focused solely on the non-medical use of the plant, from its impact on brain development to its effects on physical health.
In 1970, cannabis was classified as a Schedule I substance not because of sound science but because of its absence. Fortunately, today, only a small minority of people doubt the medical benefits of this “dangerous, illicit drug,” given the number of medical marijuana studies. But what about the health consequences of the non-medical use of the substance? What do we really know about its impact on physical, mental, and social well-being?
THC, or tetrahydrocannabinol, is the principal chemical constituent of cannabis responsible for most of its psychoactive effects. THC affects certain receptors in the brain that respond to naturally-occurring cannabinoids, in particular, anandamide (fatty acid neurotransmitter). Neurotransmitters play a role in cognition, memory and emotion. They send signals across a synapse from one neuron to another.
There are two types of cannabinoid receptors in the human body: CB1 and CB2. The first type is found in some parts of the brain. The majority of them are concentrated in the hippocampus, amygdala, cerebral cortex, and the limbic forebrain. CB1 receptors play roles in memory, emotional responses, motivation, and cognitional and motor coordination. The second type of receptors is found primarily in the body; these receptors are responsible for regulation of the immune system, liver, heart, skin, muscle functions, and many other things.
Numerous studies have already indicated that these receptors respond to THC by increasing dopamine release. This process explains the euphoric effects of cannabis.
Evidence suggests that recent consumption marijuana “are associated with substantial driving impairment, particularly in occasional smokers.” The chronic use of cannabis may cause persistent impairments in cognition and memory, especially in teenagers: cannabinoids were found to reduce the number of CB1 receptors in the parts of the brain responsible for cognition and memory.
One study compared two groups of students: regular long-term marijuana users and non-users. After conducting magnetic resonance imaging (MRI), researchers found “structural brain differences,” particularly, in the gray and white matter, in connectivity, and in global brain measures.
They also revealed that cannabis caused abnormalities in CB1-rich areas, involved in cognitive functions, and reduced the hippocampal volume; these changes negatively impacted on memory performance of the participants.
In another study, scientists used MRI to measure cortical thickness in the brains of chronic marijuana users. They found “an association between the drug use in early adolescence and reduced cortical thickness in male participants with a high polygenic risk score.” The scientists also claim that frequent and long-term cannabis use can greatly harm the white matter of the developing brain: the younger the user is, the greater is the harm weed does.
Marijuana users were found to suffer from impaired memory, to be more impulsive and aggressive compared to the non-users.
Given the fact that a child's brain is more vulnerable to the drugs than the brain of an adult, early cannabis use seems to disrupt normal brain development and lead to irreversible consequences in adulthood.
The results of the study suggest that the marijuana use in pregnant women may interfere with normal development and maturation of the fetus's brain. Kids who were exposed to cannabis before being born demonstrate “impaired attention, learning and memory, impulsivity, behavioral problems, and a higher likelihood of using cannabis when they mature.” They also have higher rates of neurobehavioral and cognitive disorders (brain diseases and mental health problems that affect learning, memory, perception, and problem solving) and are more predisposed to using the weed later in life.
According to the researchers, the negative effects may not be revealed at first but often become apparent later, over some years.
Children usually have cognitive deficits similar to those of adult cannabis users, but the symptoms are more likely to persist, and the recovery tends to be significantly longer. Moreover, most of the disorders cannot be treated at all.
The study also revealed that the teenagers who regularly used cannabis before 18 have lower IQ compared to those who became cannabis users during adulthood.
It is also important to note that age does not play such a crucial role as the frequency of use.