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Marijuana (cannabis) is the most commonly used drug worldwide. This drug contains an active substance named tetrahydrocannabinol (THC), responsible for its effects. There are divided opinions on whether marijuana has harmful health-related effects. Some authors clearly state numerous disadvantages of its use, while others are strongly against that opinion and even claim that there is no reason for marijuana to be illegal. Here we present existing evidences of side effects of marijuana presented in current literature.


Although there are variable opinions, studies have definitely shown that marijuana use can lead to addiction. This is supported by the fact that about nine percent of persons who tried marijuana develop clinical signs of addiction. Persons who smoke marijuana regularly (almost every day) have a risk of addiction estimated to be 25 to 50 percent. Symptoms of cannabis withdrawal syndrome are well recognized, and they include: insomnia, nervousness, anxiety, and craving. Special concern should be given to adolescents and young adults who start using marijuana. Namely, risk of addiction is 2 to 4 times greater in adolescents using marijuana compared to persons who start using it as adults.

Marijuana And Brain Maturation

Nervous system development is not finished until late adolescence, which takes place in the early 20s. Marijuana use during this period of brain development has been shown to be very harmful as it affects the creation of neural networks

Making connections between brain cells is the last phase of brain maturation and it occurs during a person's whole childhood and adolescence. A decreased potential of neurons to make interneural connections is the most prominent in brain areas responsible for habits and routines, self-awareness, and memory. 

These are all highly sophisticated mental functions which require a high level of neural integration. Other changes in brain tissue include lower than normal activity in prefrontal regions (area responsible for decision making, social behavior, judgment ability, etc.), and decreased volume of hippocampus (subcortical structure responsible for long-term memory).

Marijuana And Psychiatric Disorders

It is well known that persons using marijuana more commonly suffer from depression and anxiety, but scientists are not certain whether marijuana causes these disorders or it is the other way around. People who have relatives with schizophrenia already have an increased risk of this disease, but the incidence is much higher among marijuana users. Marijuana can also worsen the symptoms of schizophrenia and lower the effectiveness of medications. Same as for other mental illnesses, it is unknown whether marijuana increases risk of schizophrenia or schizophrenic patients are more prone to abusing drugs.

Effects Of Marijuana On Cancer Risk

Conclusive evidence of the increased risk of lung cancer has not been found, even in persons using marijuana regularly for more than 30 years. Some studies suggest that the risk of cancer might be higher in persons smoking both tobacco and marijuana than in persons who only smoke tobacco.

Marijuana And Driving Ability

Results of current studies show that marijuana negatively affects driving ability. This was confirmed both in driving simulation models and through statistical data about incidence of car accidents in which persons with increased THC blood levels were involved. 

The estimated risk of car accident in persons with increased alcohol levels is two to three times higher than in persons with increased THC levels, which means that alcohol affects driving ability significantly more than marijuana. Still, persons with increased THC blood levels who were involved in car accidents were found guilty three to seven times more often than persons who did not take any psychoactive substances.

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