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Marijuana is derived from the cannabis sativa or cannabis indicus plant. Marijuana is usually called cannabis by researchers. (Marijuana is Spanish for the nickname "Mary Jane.")

Hashish is a concentrated form of the marijuana resin. Marijuana can also be put into edibles, and it can be distilled down to a goo that is highly concentrated. When this is used it is called dabbing.

Historically, cannabis has been smoked, put into teas, or eaten. Since the late 1990s vaping has become more common. This is vaporization or volatilization, which extracts the active ingredients with hot air.

What is marijuana? Hashish? Dabbing? Vaping?

Marijuana first reached a peak of popularity in the United States during the late 1960s and early 1970s. Soldiers, blue-collar workers, and college students used it most.

Overall levels of marijuana use in the United States declined in the 1980s, went up again in the early 1990s, declined again in the mid 1990s, and went up again in 2000s and 2010s.

Several states in the U.S. legalized marijuana for recreational use starting with Colorado in 2014. For the first time, a majority of voters in the United States favored legalization of marijuana.

Some drugs, such as PCP and methaqualone, reach a single peak of high usage. Then government action makes them disappear.

This is possible when a drug has a key component that must be manufactured in a sophisticated laboratory. Govern­ments can track the laboratories capable of making the key ingredient and force them to stop or operate under restrictions.

That is not possible with drugs derived from natural products, such as heroin, cocaine, and marijuana. They do not require sophisticated chemicals. Their popularity goes through cycles that depend on factors like cost, availability, law enforcement efforts, and how the drugs are portrayed in mass media.

Active ingredients in marijuana resemble a neurotransmitter called anandamide, discovered in 1988. The researchers who discovered anandamide concluded that it was responsible for the reinforcing effects of marijuana. They put the word ananda (the Sanskrit word for bliss) in the chemical's name.

What is anandamide?

Scientists use the term canna­binoids to describe anandamide and similar psychoactive compounds found in marijuana. Cannabinoids appear in brain areas such as the frontal lobes and hippocampus, a pattern unlike any other psycho­active drug.

Receptors for cannabinoids are found in both the brain and the spleen of many other species, from sea urchins to rats. This suggests an "ancient–and widespread–signaling system for organisms." (Pennisi, 1993)

What is evidence that cannabinoids are an ancient signaling system?

Psychological effects of cannabis are highly variable. Marijuana is now the most popular psychoactive drug worldwide, after alcohol and tobacco.

Effects of Marijuana

First-time users of marijuana often feel nothing unless they take a potent form of the drug. Second- or third-time users may experience profound changes in conscious­ness. Colors may seem brighter, music more vivid, humor more hilarious, food more delicious.

Cannabis is widely considered a safe drug, and there are no known deaths from cannabis overdose. However, many people go to emergency rooms every year because of panic attacks brought on by using potent varieties of cannabis.

Symptoms of a panic attack brought on by cannabis include a pounding heart and anxiety. People may conclude they are dying. After reassurance by an emergency room physician, there are no long-term adverse effects.

Why does cannabis send so many people to emergency rooms?

The specific cause of cannabis anxiety attacks is first-time use of a high potency cannabis product. It can occur whether the cannabis is smoked, vaporized, or eaten.

New York Times columnist Maureen Dowd provided an example of what can happen to a novice user. She visited Colorado in 2014, shortly after the state legalized cannabis, to give it a try. Dowd was not a smoker, so she bought some cannabis-infused chocolate bars. As she reports:

Sitting in my hotel room in Denver, I nibbled off the end and then, when nothing happened, nibbled some more...

What could go wrong with a bite or two?

Everything, as it turned out.

Not at first. For an hour, I felt nothing. I figured I'd order dinner from room service and return to my more mundane drugs of choice, char­donnay and mediocre-movies-on-demand.

But then I felt a scary shudder go through my body and brain. I barely made it from the desk to the bed, where I lay curled up in a hallu­cinatory state for the next eight hours...

It took all night before it began to wear off, distressingly slowly. The next day, a medical consultant at an edibles plant where I was conducting an interview mentioned that candy bars like that are supposed to be cut into 16 pieces for novices; but that recommend­ation hadn't been on the label. (Dowd, 2014)

In retrospect, Dowd made several mistakes. She took a large dose (inadvertently) of a variety she had never encountered before.

Despite being a beginner, she did not seek the guidance of a more exper­ienced person until the next day. Then she found out she took sixteen times the recommended amount.

Why are anxiety attacks more likely when consuming a variety of cannabis for the first time? The drug has an extremely complex makeup.

There are over 400 chemicals in marijuana, 61 of which are unique to the cannabis plant (those are called cannabinoids). The effect of each sub-type of cannabis is slightly different.

Users adapt to particular varieties. A new variety represents a different biochemical challenge to the brain. This is when a panic attack occurs: when trying a variety new to the user and very potent.

The chemistry of the plant also changes during its life-cycle. For example, a young plant may produce a more cerebral mental state, while the same plant when older may cause sleepi­ness or anxiety.

What are sources of variation in marijuana?

Medical marijuana experts know about these differences. They guide patients to the variety they need to get sleep, reduce anxiety, improve appetite, reduce pain, or other desired effects.

A beginner taking "pot luck" with flowertop offered by a friend does not know what to expect. Encountering a potent variety for the first time makes an anxiety reaction more likely.

For those (like Dowd) sampling the drug for the first time where it is legal, the safest approach is to begin with a low dose, a third or a quarter of what might be consumed by an experienced user. The result might be only a mild alteration in consciousness, but that is preferable to an anxiety attack.

Why do anxiety attacks tend to occur after the first encounter with a new form of cannabis?

Cannabis is famous for stimulating appetite ("the munchies"). This inspired chemists to look for compounds that might curb appetite by blocking cannabinoid receptors in the brain.

A team of 10 researchers from the Psychology Department at the University of Connecticut showed this was possible. They found a cannabinoid receptor antagonist (a substance opposing the action of cannabinoid receptors) that reduced food consumption in laboratory rats (McLaughlin et al., 2003).

What are common effects of marijuana? How did cannabinoid antagonists affect rats?

Such a product could be very valuable if marketed to humans as a diet pill. Unfortunately, the appetite-suppressing cannabinoid had an unpleasant side-effect in humans: it produced mild depression.

Research on rats and mice suggests an "anti-aggressive effect" of marijuana (Miczek, 1978). Violence among marijuana smokers is rare unless it is combined with other drugs like alcohol or cocaine.

A famous passage from the La Guardia commis­sion report in the 1930s noted Harlem residents who smoked "reefers" were not more likely to commit crimes. They were likely to be found on rooftops with friends, commenting on the appearance of the city and sky at night.

Health Consequences of Cannabis Use

In 1969 researchers at the National Institutes of Mental Health felt it was necessary to seek a "long-term, multi-disciplinary study of chronic marijuana smokers who weren't taking a lot of other drugs." The result was a two-year study involving more than 2,000 regular marijuana users in Jamaica.

In the Jamaica study, 30 male ganja users were matched with 30 non-users of the same age. Men in the ganja-using group averaged seven pounds lighter and tended to have bloodshot eyes.

Other than that, few differences turned up in biological or intellectual tests. Testosterone texts in the two groups were identical.

The only medical difference was a tendency to hyposia (reduced oxygen delivery to tissues) in the ganja-using group, probably due to the tobacco in their smoking mixtures. Research with long-term marijuana users in Costa Rica produced similar conclusions.

What were the findings of the "Jamaica study"?

Studies by Robert Block and colleagues in the early 1990s suggested that chronic marijuana use could have damaging effects on cognitive abilities (Block & Ghoneim, 1993). They located groups of people who abilities were matched during 4th grade, as measured by the Iowa tests frequently given to American school children.

By 12th grade, individuals smoking marijuana seven or more times weekly had lower scores for math and verbal expression. Those using marijuana one to six times weekly showed no differences from the control group.

Block (1996) in an editorial in JAMA (Journal of the American Medical Association) said these and similar findings by Pope & Yurgelun-Todd (1996) justified concerns but should not be exaggerated. "There is far more extensive, consistent evidence of cognitive deficits associated with heavy use of alcohol relative to marijuana" (Block, 1996).

Marie and Zolitz (2015) took advantage of a one-time event in which the city of Maastricht restricted cannabis access by nationality. Studying 54,000 course grades of students, the researchers found that grades went up among students who no longer had legal access to cannabis.

The students were 5% more likely to pass a course, on the average, than they were when cannabis was available to them legally. These effects were more pronounced in students who were female and those who were younger. The researchers speculated that those sub-groups were less likely to obtain cannabis illegally during the ban.

One of the most ambitious long-term studies of cannabis effects on health was conducted in New Zealand by Meier, Caspi, Cerda, and colleagues (2016). Participants belonged to a group of 1037 individuals born in 1972 and 1973 and followed to age 38.

A full 95% of the initial group was tracked for all 38 years. They were tested in numerous ways at regular intervals.

The only health problem associated with cannabis use was a higher incidence of gum disease. Tobacco use, by contrast, was associated with worse lung function, systemic inflammation, and a decline in health between age 26 and 38.

What are the results of long-term studies of cannabis users?

Bechtold, Simpson, White, and Pardini (2015) reported on a similar large scale, long-term study in the U.S. They looked at four groups that varied dramatically in the amount of cannabis they consumed. There were no differences between the groups on measures of health. The researchers concluded:

Overall, data from this sample provide little to no evidence to suggest that patterns of mari­juana use from adolescence to young adulthood, for the Black and White young men in the present study, were negatively related to the indicators of physical or mental health studied here. (p.560)

In particular, the researchers found no evidence that cannabis increased the risk of psychosis (serious mental illness involving delusions) at any level of consumption. The researchers paid attention to this possibility, because some researchers, particularly in Britain, suggested an increased risk of psychosis in heavy cannabis users.

Those warnings were based on self-report data from people already suffering from psychosis, indicating prior cannabis use. Doctors also said they noticed people with psychosis who used cannabis in the past tended to continue to use it after their diagnosis. It seemed to make their problems worse.

The Bechtold et al. research looked for an increase in psychosis among cannabis users but did not find any. Their sample consisted of people who did not already suffer from psychosis. It remains possible that people at serious risk of psychosis, a small percentage of the total population, are more likely to be destabilized by cannabis.

What "remains possible" about the relationship of cannabis to psychosis?


Bechtold, J., Simpson, T., White, H. R., & Pardini, D. (2015) Chronic adolescent marijuana use as a risk factor for physical and mental health problems in young adult men. Psychology of Addictive Behaviors, 29, 552-563.

Block, R. I. & Ghoneim, M. M. (1993) Effects of chronic marijuana use on human cognition. Psychopharm­acology, 110, 219.

Block R. I. (1996) Does Heavy Marijuana Use Impair Human Cognition and Brain Function? [Editorial] Retrieved from:

Dowd, M. (2014, June 3) Don't harsh our mellow, Dude. New York Times,

McLaughlin, P. J., Winston, K., Swezey, L., Wisniecki, A., Aberman, J., Tardif, D. J., Betz, A. J., Ishiwari, K., Makriyannis, A., & Salamone, J. D. (2003) The cannabinoid CB1 antagonists SR 141716A and AM 251 suppress food intake and food-reinforced behavior in a variety of tasks in rats. Behavioral Pharmacology, 14, 583-588.

Meier, M. H., Caspi, A., Cerda, M., Hancox, R. J., Harrington, H., Houts, R., Pourton, R., Ramrakha, S., Thomson, V. M., & Moffitt, T. E. (2016) A Longitudinal Comparison of Persistent Cannabis vs Tobacco Users. JAMA Psychiatry, 73, 731-740.

Pennisi, E. (1993, Sept 11) THC: An ancient internal signal system of organisms. Science News. p. 165.

Pope, H. G. & Yurgelun-Todd, D. (1996) The residual cognitive effects of heavy marijuana use in college students. JAMA, 275, 521-527.

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