April 24, 2015

By Medical Discovery News

It is now legal to use marijuana (recreationally and/or medically) in more than 20 states and the District of Columbia, and as more places debate legalizing the substance, more people are asking about its consequences on human health. There are many myths and misconceptions out there, but this is what science has to say about the subject.

As with all substances, the health effects depend on the potency, amount, and a person’s age. An independent scientific committee in the United Kingdom evaluated how harmful various drugs were based on 16 criteria and ranked heroin, crack cocaine, and methamphetamine as the most harmful drugs to individuals using them, and ranked alcohol, heroin, and crack cocaine as the drugs that cause the most harm to others. Marijuana ranks eighth, with slightly more than one-quarter the harm of alcohol.

Short-term use is associated with impaired short-term memory, making it difficult to learn and retain information while under the influence. Short-term use can also impair motor coordination, interfering with tasks such as driving. The overall risk of an accident doubles if a person drives soon after using marijuana. In comparison, those with blood alcohol levels above the legal limit are five times more likely to have an accident, and the combination of alcohol and marijuana is higher than either one alone.

Long-term or heavy use is associated with diminished life satisfaction and achievement overall. At high doses, marijuana can cause paranoia and psychosis, and long-term marijuana use increases the risk of developing schizophrenia or other chronic psychotic illnesses. Nine percent of all marijuana users, or 2.7 million people, develop an addiction to it. That figure jumps to 25-50 percent for those who use marijuana daily, and 17 percent of people who begin using marijuana as adolescents become addicted. Cannabis withdrawal syndrome is real and includes symptoms of irritability, sleep disturbance, dysphoria, craving, and anxiety.

Adults who occasionally use marijuana do so with little to no risk, but adolescent brains are not fully developed, making them more vulnerable to the adverse effects of marijuana. Using marijuana during adolescence can alter brain development, causing impaired cognition and lower IQs. This is probably because the active ingredient in marijuana, tetrahydrocannabinol, affects the brain’s ability to make connections between neurons in certain regions of the brain. Adolescent marijuana users also have a smaller hippocampus, which is important in learning and memory, and a less active prefrontal cortex, which is important in cognitive tasks such as planning and problem-solving.

Since acute marijuana intoxication can impair cognitive functions for days, students who use marijuana may function well below their natural abilities, causing academic difficulties. High school dropouts do report higher marijuana usage than their peers. Some evidence suggests that these cognitive impairments could be long-lasting or permanent in long-term users who started at younger ages, which can impact their abilities to succeed academically and professionally.

There is no clear association between long-term marijuana use and any deadly disease, although chronic marijuana smokers have increased rates of respiratory infections and pneumonia and an increased risk of heart attack and stroke. The effects of marijuana on a developing embryo and the effects of second-hand or third-hand marijuana smoke have not been well-studied, but as marijuana legalization continues to be an issue the science behind it will as well.

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