It's April 20. For those not in the know, 4/20 is the unofficial holiday that pot smokers and marijuana-legalization activists around the world celebrate by lighting up.
The plant, best-known for its "feel-good" effects and touted for its uses for diseases, can damage our bodies and minds.
The high you get from marijuana mostly comes from a chemical called tetrahydrocannabinol, or THC, which is found in varying amounts in different strains of cannabis.
Another important compound is cannabidiol, or CBD, thought to cause many of the medical effects of marijuana. There are more than 70 other chemicals in marijuana that could cause effects on the brain and body that haven't been well studied.
Most of THC's effects happen in the brain, where the chemicals in the plant interact with receptors on brain cells called cannabinoid receptors. Our bodies actually make chemicals similar to THC, used in normal brain function and development. THC co-opts these natural pathways to produce most of its effects, which are varied and depend on how much and how often someone uses pot.
Marijuana makes us feel good.
When THC hits brain cells, it causes them to release dopamine, a feel-good brain chemical. This is a part of the brain's reward system, which makes you feel good when you do things that ensure the survival of yourself and your offspring. These things include eating and having sex.
When over-excited by drugs, the reward system creates feelings of euphoria.
But too much of a good thing can become a problem, as the more often you trigger this feeling, the less you can feel happiness for other "rewarding" experiences. It takes a lot of pot use to get to this point, though.
In a recent study of people who had smoked nearly five joints a day, five days a week, for more than a decade, researchers saw that heavy pot smokers had weaker responses to the stimulant methylphenidate, which is used to treat attention-deficit/hyperactivity disorder, than nonusers. The stimulant gave them a less intense "high."
It can be addictive.
Because of those feel-good effects, extended, heavy use of marijuana can be addictive or cause dependence. That doesn't mean anyone who tries marijuana will become addicted — most causal pot users most likely aren't — but there are some factors that could increase the likelihood of addiction.
New studies have found that pot can be more addictive when used in combination with nicotine (in the form of blunts) or when used through a vaporizer or other means, which may be more potent than smoking. According to researchers, this could mean that physiological effects of vaporized marijuana extracts could be very different from those of smoked marijuana, since the vaporized marijuana contains mostly THC, the main psychoactive compound.
A study in the journal Addictive Behaviors researchers found that compared to marijuana smokers, users who ingest hash oil using a wax, called "dabbing," or by inhaling marijuana oil using a "vape pen," may more rapidly develop tolerance and may also have a greater risk of withdrawal — two signs of addiction.
It blocks memory formation.
The active ingredient in marijuana acts in the part of the brain called the hippocampus to alter the way information is processed and how memories are formed. Animal studies have shown that this is particularly true while the brain is still developing.
This is specifically why the legal smoking age is 21 in the states that have legalized it.
This blockage of memory formation can cause cognitive impairment in adulthood if use happens during adolescence, at least in rats. It can also quicken age-related brain cell loss, though some studies have suggested that marijuana may be able to slow the progression of Alzheimer's disease.
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