Pharmacology of Cannabis.

2009.05.05

The main effects of cannabis are on cognitive functioning. These effects are exerted through cannabinoid receptors that are located in both the hippocampus and cortex of the brain. High densities of cannabinoid receptors also appear in the basal ganglia and cerebellum; this is consistent with the finding that cannabinoids interfere with coordination.

THC is lipid soluble and is stored readily in fatty tissues. As a consequence, traces of cannabinoids can be found slowly escaping from fat tissues, and thus be present in urine, up to two to three months after use of cannabis; therefore, a positive urine test for cannabis is not an absolute indication of recent cannabis use, although higher urinary cannabinoid levels will provide an indication of more recent use.

The Acute Effects of Cannabis Use

The use of cannabis can result in a ‘high’ or altered state of consciousness. This state is characterized by emotional changes such as mild euphoria, perceptual changes, and heightened sensory experiences, e.g. listening to music, eating, watching films, etc.

The effects of cannabis are highly variable, and depend upon the following.

  • The dose

  • Administration route

  • Prior experience with the drug

  • Concurrent drug use

  • The user’s expectations of the effects of the drug

  • The social environment and mood of the user

 

Acute Cognitive Effects

Cannabis use can affect cognition, causing short term memory impairment.

Acute Psychiatric Effects

Some individuals have reported unpleasant effects from cannabis use ranging from anxiety to panic attacks, depressed mood, and a fear of ‘going crazy’. However, these effects are mostly found in the inexperienced user, and can usually be managed with reassurance and support.

Psychotic symptoms such as delusions and hallucinations can occur in individuals using very high doses of THC, although this is a rare occurrence. These symptoms may also be experienced at lower doses by people who have a vulnerability to psychosis.

Acute Physical Effects

The most immediate effect of cannabis use is an increase in heart rate which can last up to three hours. In the young, healthy user, cardiovascular changes are generally clinically insignificant. However, cannabis may adversely affect patients with ischemic heart disease, hypertension, and cerebrovascular disease. In the susceptible patient, cannabis acts to increase catecholamine production which can cause arrhythmias, and increase heart rate resulting in angina. Postural hypotension may also be an acute effect of cannabis use.

Acute Psychomotor Affects

Coordination and reaction time are impaired during intoxication with cannabis. Of particular concern is the impact of cannabis intoxication on driving ability. Some studies suggest an increased risk of motor vehicle accidents among individuals who drive when intoxicated by cannabis. This increased risk may be due to the combined use of alcohol and cannabis. Therefore, it is pragmatic to advise cannabis users not to drive a motor vehicle while under the influence of cannabis.

The Effects of Chronic Cannabis Use on Health

Evidence suggests that cannabis smoke is mutagenic. It shares many of the same carcinogens as cigarette smoke. The major cancers arising from cannabis use are those involving the respiratory tract and the aero digestive tract. In addition, there is evidence that habitual marijuana use causes airway abnormalities affecting mainly the large airways; tobacco use alone affects predominantly the peripheral airways and alveoli. Research suggests that long-term cannabis use may cause chronic bronchitis.

There is a possibility that chronic, heavy cannabis smoking may have subtle effects on the cardiovascular system.

The Psychological Effects of Chronic Cannabis Use

A major concern regarding the psychological effects of cannabis use is the impact it has on motivation, particularly in adolescence. Chronic use interferes with developmental tasks, such as educational achievement, separation from parents, forming peer relationships, and making important life choices.

Reproductive Effects

Studies carried out on male animals have shown that cannabis use reduces plasma testosterone levels, retards sperm maturation, reduces sperm count and sperm motility, and increases the rate of abnormal sperm production. Studies on human females have conflicting results. In female animals, studies have shown that chronic cannabis use interferes with ovulation and probably has an inhibitory effect on the female reproductive system.

Pregnancy

Pregnant women who smoke cannabis are at risk of a shorter gestation period and giving birth to low weight babies. Women who smoke cannabis at the time of conception or while pregnant may increase the risk of birth defects, although research is inconclusive. Women should be encouraged to abstain from cannabis when trying to conceive and during pregnancy.