The Science behind Marijuana


By Song My Hoang

Investigating how the drug used by 42 percent of Americans works

With the advent of legalization of marijuana for medicinal and recreational purposes, scientists have to critically reevaluate its potential short-term and long-term effects.

Marijuana, also known as cannabis, is the world’s most widely used illicit substance.  In 2012, more than 42 percent of the population in the U.S. admitted to trying marijuana.

Marijuana usage is particularly high among youth and young adults; 56 percent of young adults in the U.S. admitted to using marijuana at least once in their lifetime.

The primary psychoactive compound in marijuana is tetrahydrocannabinol (THC). THC mimics the structure of endocannabinoids, which are molecules that the human body produces naturally.

Endocannabinoids are intracellular messengers that interact with endogenous cannabinoid receptors, CB1 and CB2. CB1 receptors are mainly expressed in the central and peripheral nervous systems while CB2 receptors are mainly expressed in the immune system.

The activation of CB1 receptors produces circulatory and psychotropic effects that are common to cannabis ingestion while the activation of the CB2 receptor does not.

CB1 receptors are highly expressed in regions of the brain where they regulate neuronal excitability and synaptic transmission. This reflects the importance of the cannabinoid system in motor control, memory processing and pain modulation.

In particular, CB1 receptors are concentrated in the frontal cortex, basal ganglia, hippocampus and cerebellum, which are areas of the brain that govern pleasure, movement, learning, memory and pain.

As the structure of THC resembles that of endocannabinoids, the uptake of marijuana induces the activation of CB1 receptors. This culminates in both abnormally elevated and low levels of various neurotransmitters, molecules that brain cells use to communicate with each other. The result is the well-known “high” experienced by marijuana users.

Marijuana’s continued popularity raises a particular concern because the drug might hinder the ongoing maturation of the adolescent brain.

Studies have shown that individuals under the influence of marijuana perform worse on tests of working memory, the ability to temporarily retain information in one’s mind.

Participants in these studies show greater difficulty remembering and reciting short lists of random words and numerals.

Researchers at Imperial College London, University College London and King’s College London published a study showing that long-term cannabis users tend to produce less dopamine, a chemical in the brain linked to motivation. They used PET brain imaging to observe dopamine production in the striatum of 19 regular cannabis users and 19 non-users. The lowest dopamine levels were seen in cannabis users.

Research has further revealed that cannabis weakens motor coordination and concentration, which interferes with the individual’s ability to respond to external stimuli.

In a driving simulation and closed-course studies, marijuana users were slower to hit the brakes and worse at safely changing lanes. There is still debate about at what stage these impairments may lead to traffic accidents.

The administration of marijuana for certain medical conditions is considered safe to temporarily alleviate symptoms. In the past decade, the scope of research on marijuana has increased dramatically.

Research has employed cannabis or cannabis-based extracts that are delivered by smoking, vaporization, oral intake, sublingual or mucosal routes.

Cannabis exerts several therapeutic effects; it has antispastic, antiemetic and neuroprotective actions.

Novotna et al.’s study, published in the European Journal of Neurology, examined the treatment of spasticity in multiple sclerosis. Patients participated in a single-blind period of therapy, where 48 percent of the patients responded to the treatment. Compared with the placebo, the cannabis extract dramatically reduced overall spasticity as well as the frequency of spasms in patients.

Numerous studies have been carried out to demonstrate that cannabinoids are effective against chemotherapy-related nausea and vomiting, as were the standard antiemetics.

Clinical trials at the University of California Center for Medicinal Cannabis Research investigated the short-term efficacy of smoked cannabis for neuropathic pain. The trial enrolled patients with mixed neuropathic pain due to peripheral or central dysfunction of the nervous system, such as traumatic focal nerve or spinal cord injury. Patients were allowed to continue their usual regimen of analgesics.

Results indicated that marijuana reduced pain intensity as patients reported 34 percent to 40 percent decrease on cannabis compared to 17 percent to 20 percent on the placebo.

It is crucial to continue extensive research on marijuana in order to provide conclusive results about its helpful and harmful effects as the drug takes a bigger share of the spotlight at both the state and federal levels, regarding both recreational and medicinal growing, selling and using.


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