Pharmacology of Marijuana

There are a wide variety of different user experiences with marijuana, depending upon the potency of the drug taken. In general, smoking marijuana relaxes the user and elevates her mood. Users can shift between contemplation and hilarity depending on their surroundings.

Marijuana is the Indian hemp plant, Cannabis sativa, or the crude drug composed of its leaves and flowers. It is usually dried and crushed and put into pipes or formed into cigarettes (reefers, or joints) for smoking. The drug–known by a variety of other names, including pot, tea, grass, and weed–can also be added to foods and beverages. Marijuana varies in potency, depending on where and how it is grown, prepared for use, or stored. The active ingredient, tetrahydrocannabinol (THC), is present in all parts of both the male and female plants but is most concentrated in the resin (cannabin) in the flowering tops of the female.

[The following is excerpted from "Drug Wars" FRONTLINE, WGBH, Boston, 2000 www.pbs.org/wgbh/pages/frontline]

Marijuana acts on specific cannabinoid receptors in the brain. Psychological effects tend to be predominant; the user commonly experiences a mild euphoria. Alterations in vision and judgment result in distortions of time and space. Acute intoxication may occasionally induce visual hallucinations, anxiety, depression, extreme variability of mood, paranoid reactions, and psychoses lasting from four to six hours.

Physical effects include reddening of the eyes, dryness of the mouth and throat, moderate increase in the rapidity of the heartbeat, tightness of the chest (if the drug is smoked), drowsiness, unsteadiness, and muscular incoordination.

In the late 1980s researchers discovered a receptor for THC and THC-related chemicals in the brains of certain mammals, including humans. This finding indicated that the brain naturally produces a THC-like substance that may perform some of the same functions that THC does. Such a substance subsequently was found and named anandamide, from “ananda,” the Sanskrit word for bliss.

When marijuana is smoked, the blood supply of the lungs absorb the THC. The blood then moves to the heart where it increases the heart rate. If the marijuana is eaten, less THC gets to the brain and takes longer to get there. The amount of THC in the body would be less for the amount of marijuana eaten, however, since it takes longer to work, users are likely to consume more marijuana than they would normally smoke. High levels of THC can cause hallucinogen-like experiences that smokers are less likely to feel.

Chronic use does not establish physical dependence, nor, upon withdrawal, does the regular user suffer extreme physical discomfort (such as that associated with narcotics), but its use may be psychologically habituating. Since THC remains in the body, it has been found to have residual effects on cognitive functions (including memory) up to 48 hours after smoking.

However, there is no evidence that these effects last longer than two days. Chronic marijuana smokers can experience lung problems and generally do not produce as much airflow as nonsmokers do.