There is a lot of push for legalization of recreational use of marijuana. In fact, I read one article on the odyssey that made the claim it was completely harmless. I'm not making the claim for legalizing recreational use or making it illegal; I do however feel it important for people to be informed about what exactly happens when marijuana is used. This is a brief overview of some of the bodily impacts it can have.
Marijuana is a a stimulant as well as a depressant; this means that as a depressant it slows brain activity, but at the same time as a stimulant elevates mood and can create feelings of euphoria and elevate heart rate. Often, marijuana can be mixed with other drugs like cocaine to intensify the feelings. When mixed, the effects can be extremely dangerous and cause major cognitive deficits or even death. Marijuana by itself is not nearly as dangerous, however is not harmless. The drug has multiple chemicals within it, but the most well known is delta-9-tetrahydrocannabinol or commonly referred to as THC.
There are different grades of the drug, hash oil is typically known to have highest amount of THC. When the smoke is inhaled into the lungs the absorption rate is much higher as opposed to ingesting the drug; this is because of the small amount of time it takes for it to get into the blood stream and from there to the brain. According to the fourth edition of the book Buzzed, THC stays in the body long after the high has worn off. "about half of the THC is still in the blood 20 hours after smoking". They also state that when the blood containing the THC reaches the liver a portion of the THC is converted into various other compounds that will stay in the body for days after. THC also stays in the body for long periods of time because it can be stored in fat. The fact that THC is present in the body for a long period of time after the initial "high" is evidence for longer lasting cognitive impacts. The hippocampus, a part of the brain that is essential for memory recall has quite a few cannabinoid receptors, which is part of the reason this drug goes hand in hand with a loss of memory function.
One animal study stated in the book Buzzed; shows a difference is memory function (likely related to the hippocampus) in younger animals versus matured animals. The younger animals had a much greater negative memory impact compared to the adult animals. Another difference is a decrease in negative side affects in the younger animals like paranoia. Another area of the brain affected is the cerebellum which is associated with fine motor movement. This is part of the reason why it is dangerous to operate a car under the influence of marijuana. Overall studies show a memory and learning impairment in regular smokers.
Besides the brain affects, smokers of marijuana tend to have a higher heart rate and decrease the efficiency of each beat. One not so surprising impact is on the lungs. I think very few people will argue smoke of any kind being inhaled regularly is not good for the lungs. Long term use of Marijuana shows a lack of airflow compared to non-smokers. Another more surprising fact stated in the book Buzzed is a similarity in marijuana smoke to tobacco smoke. One carcinogen that is present in marijuana is benzopyrene. At this time there are no direct link to lung cancer, but smokers are more likely to be predisposed to lung cancer; due to DNA damage in lung cells.
Marijuana, while not the "heaviest" drug on the market, still posses its risks that affect the brain. This article is not in regards to medicinal uses, legislation. This is just a few things on health risks of regular marijuana use.