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Marijuana (Cannabis)

by Patrick G. O’Connor, MD, MPH

Marijuana is a euphoriant that can cause sedation or dysphoria in some users. Overdose does not occur. Psychologic dependence can develop with chronic use, but very little physical dependence is clinically apparent. Withdrawal is uncomfortable but requires only supportive treatment.

Marijuana is the most commonly used illicit drug; it is typically used episodically without evidence of social or psychologic dysfunction.

In the US, marijuana is commonly smoked in cigarettes, made from the flowering tops and leaves of the dried plant, or as hashish, the pressed resin of the plant. Much less commonly, marijuana is taken orally. Dronabinol, a synthetic oral form of the active ingredient, Δ-9-tetrahydrocannabinol (THC), is used to treat nausea and vomiting associated with cancer chemotherapy and to enhance appetite in AIDS patients.


Δ-9-THC binds at cannabinoid receptors, which are present throughout the brain.

Chronic effects

Any drug that causes euphoria and diminishes anxiety can cause dependence, and marijuana is no exception. However, heavy use and reports of inability to stop are unusual. Critics of marijuana cite much scientific data regarding adverse effects, but most claims of significant biologic effect are unsubstantiated. Findings are sparse even among relatively heavy users and in areas intensively investigated (eg, immunologic and reproductive function). However, high-dose smokers develop pulmonary symptoms (episodes of acute bronchitis, wheezing, coughing, and increased phlegm), and pulmonary function may be altered, manifested as large airway changes of unknown significance. Even daily smokers do not develop obstructive airway disease. There is no evidence of increased risk of head and neck or airway cancers, as there is with tobacco. In a few case-control studies, diminished cognitive function was identified in small samples of long-term high-dose users; this finding needs to be confirmed. A sense of diminished ambition and energy is often described.

The effect of prenatal marijuana use on neonates is not clear. Decreased fetal weight has been reported, but when all factors (eg, maternal alcohol and tobacco use) are accounted for, the effect on fetal weight appears less. THC is secreted in breast milk. Although harm to breastfed infants has not been shown, breastfeeding mothers, like pregnant women, should avoid using marijuana.

Symptoms and Signs

Intoxication and withdrawal are not life threatening.

Acute effects

Within minutes, smoking marijuana produces a dreamy state of consciousness in which ideas seem disconnected, unanticipated, and free-flowing. Time, color, and spatial perceptions may be altered. In general, intoxication consists of a feeling of euphoria and relaxation (a high). These effects last 4 to 6 h after inhalation.

Many of the other reported psychologic effects seem to be related to the setting in which the drug is taken. Anxiety, panic reactions, and paranoia have occurred, particularly in naive users. Marijuana may exacerbate or even precipitate psychotic symptoms in schizophrenics, even those being treated with antipsychotics.

Physical effects are mild in most patients. Tachycardia, conjunctival injection, and dry mouth occur regularly. Concentration, sense of time, fine coordination, depth perception, tracking, and reaction time can be impaired for up to 24 h—all hazardous in certain situations (eg, driving, operating heavy equipment). Appetite often increases.


Cessation after 2 to 3 wk of frequent, heavy use can cause a mild withdrawal syndrome, which typically begins about 12 h after the last use. Symptoms consist of insomnia, irritability, depression, nausea, and anorexia; symptoms peak at 2 to 3 days and last up to 7 days.


  • Clinical evaluation

Diagnosis is usually made clinically. Drug levels are not measured. Most routine urine drug screens include marijuana (see Drug Testing).


  • Supportive measures

Treatment is usually unnecessary; for patients experiencing significant discomfort, treatment is supportive. Management of abuse typically consists of behavioral therapy in an outpatient drug treatment program.

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