Merck Manual

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Gerald F. O’Malley

, DO, Grand Strand Regional Medical Center;

Rika O’Malley

, MD, Grand Strand Medical Center

Reviewed/Revised Dec 2022

Marijuana (cannabis) is a drug made from the plants Cannabis sativa and Cannabis indica that contain a psychoactive chemical called delta-9-tetrahydrocannabinol (THC).

  • Marijuana produces a dreamy state, a sense of well-being, and distorted perceptions.

  • People can develop psychologic dependence when they use marijuana for a long period of time.

  • Stopping the drug causes only mild symptoms.

  • Marijuana can be detected in urine for days to weeks after it was used.

  • Treatment involves counseling, which is effective only when people are motivated to stop.

Marijuana (cannabis) use is widespread in the United States; typically, marijuana is used periodically without evidence of social or mental health issues.

In the United States, marijuana is commonly smoked in the form of cigarettes (joints) made from the stems, leaves, and flowering tops of the dried plant (Cannabis sativa or Cannabis indica). Marijuana is also used as hashish, the pressed resin (tarry substance) of the plant. The legalization of marijuana has led to a market for products that can be eaten and vaporized in e-cigarettes. There are also a variety of forms that can be applied to the skin as tinctures, lotions, or sprays.

The active ingredient of marijuana is delta-9-tetrahydrocannabinol (THC). Dronabinol, a synthetic form of delta-9-THC, is used to relieve nausea and vomiting caused by chemotherapy drugs and to enhance appetite in people with AIDS.

Most people use marijuana intermittently and without developing noticeable social or psychologic dysfunction or dependence. However, some people become dependent on marijuana.

Symptoms of Marijuana Intoxication

Marijuana causes immediate and sometimes long-term symptoms.

Immediate effect

Marijuana slows brain activity, producing a dreamy state in which ideas seem disconnected and free-flowing. It is mildly psychedelic, causing time, color, and spatial perceptions to distort and be enhanced. Colors may seem brighter, and sounds may seem louder. The sense of euphoria and relaxation is called a high.

Marijuana generally relieves tension and provides a sense of well-being. The sense of exaltation, excitement, and inner joyousness (a high) seems to be related to the setting in which the drug is taken—such as whether the person is alone or in a group and what the prevailing mood is.

Coordination, reaction time, depth perception, and concentration may be impaired for 24 hours after marijuana use, so driving or operating heavy equipment is dangerous during this time. Other effects include an increased heart rate, bloodshot eyes, increased appetite, and dry mouth. These effects usually last 4 to 6 hours after inhalation.

Some people, especially those who have not used marijuana before, experience anxiety or feel panicky or paranoid. Marijuana may worsen or trigger psychosis (loss of contact with reality) in people with schizophrenia Schizophrenia Schizophrenia is a mental disorder characterized by loss of contact with reality (psychosis), hallucinations (usually, hearing voices), firmly held false beliefs (delusions), abnormal thinking... read more .

Long-term effects

People who use large quantities of marijuana for a long time may develop breathing problems such as

  • Bronchitis

  • Wheezing

  • Coughing

  • Increased phlegm

  • Abdominal pain and cyclic vomiting syndrome

However, people who smoke marijuana do not develop obstructive airway disease, even those who smoke daily. There is no evidence of increased risk of head and neck or airway cancers, as there is with tobacco.

Recent studies suggest that marijuana use begun in adolescence can lead to cognitive impairment and changes in the brain.

Cannabinoid hyperemesis is a recently described syndrome in which long-time users of marijuana have alternating bouts of nausea and vomiting. The syndrome usually resolves within 48 hours. Taking hot baths provides some relief and is the biggest clue for doctors to diagnose the condition.

Some studies show that women who smoke marijuana are less likely to conceive. Those who become pregnant may have smaller babies than nonusers, but the effect seems small. Delta-9-THC passes into breast milk, but no harmful effects have been detected in babies. Nonetheless, women who are pregnant, trying to get pregnant, or breastfeeding are advised not to use marijuana.

Men who smoke marijuana frequently have a reduced sperm count, resulting in a possible decrease in fertility.

Withdrawal symptoms

Marijuana is eliminated from the body slowly over several weeks, so withdrawal symptoms tend to be mild. After a few weeks of heavy, frequent use, abruptly stopping causes symptoms that begin about 12 hours later and last up to 7 days. Symptoms include

  • Insomnia

  • Irritability

  • Depression

  • Nausea

  • Loss of appetite

Diagnosis of Marijuana Intoxication

  • Urine test

A urine test can detect THC for several days or weeks after it is used, even in casual users. In regular users, the test may detect the drug for even longer while the drug is slowly released from body fat. Urine testing is an effective means of identifying marijuana use, but a positive result means only that a person has used marijuana. It does not prove that the user is currently impaired (intoxicated).

Treatment of Marijuana Intoxication

  • Observation and monitoring until the person is sober

  • Counseling and drug treatment

For people who want to stop using marijuana, counseling, behavior modification, and drug treatment programs may be helpful. However, success relies heavily on their motivation to stop and, for some users, on their willingness to disassociate from their social circle of regular users.

Some chronic users of marijuana develop cyclic vomiting syndrome (recurrent nausea and vomiting). Doctors may treat this with IV fluids, antinausea medications, and sometimes capsaicin creams rubbed on the abdomen.

More Information

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Marinol, SYNDROS
Arthricare for Women, Arthritis Pain Relieving, Capsimide, Capzasin-HP, Capzasin-P, Castiva Warming, Circatrix, DermacinRx Circata, DermacinRx Penetral, DiabetAid, Qutenza, Zostrix, Zostrix HP, Zostrix Neuropathy
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