ACUTE INTOXICATION — The onset of acute marijuana intoxication is within minutes when smoked and the effects last for three to four hours.

Signs and symptoms — Physiologic signs of acute intoxication include:

  * Tachycardia
  * Elevated blood pressure
  * Elevated respiratory rate
  * Conjunctival injection
  * Dry mouth
  * Increased appetite
  * Impaired reaction time.

Psychologic signs of intoxication include:

  * Euphoria
  * Time distortion
  * Anxiety
  * Depression
  * Impaired short-term memory
  * Paranoia
  * Mystical thinking

Impairment of concentration and motor performance last for 12 to 24 hours due to accumulation of marijuana in fatty tissue, with slow release of THC from fatty tissue stores and enterohepatic recirculation.

Thus, a marijuana user may think that he or she is no longer impaired several hours after use when the acute mood altering effects wear off. However, impairment of cognition, coordination, and judgment lasts much longer than the subjective feeling of being “high.” Impairment is intensified by combination with other drugs, especially alcohol.

These findings may help explain the observation that fatal traffic accidents occur more often among individuals who test positive for marijuana. International studies have shown rates of positive urine or blood tests for marijuana varying from 10 to 57 percent in impaired or injured drivers. Screening for marijuana and other drugs of abuse, in addition to alcohol, may be a useful adjunct to standard roadside sobriety testing.

Drug testing — Testing for drugs of abuse can be performed on multiple types of samples, including urine, blood, breath, hair, saliva, and sweat. Urine testing is most widely used. Marijuana metabolites are stored in adipose and can be excreted in the urine for several days. Therefore, a positive urine test does not necessarily prove current impairment. Nonetheless, a positive test does indicate recent marijuana ingestion and should lead to a determination of patterns of use, and potential for dependence. Marijuana is the most common drug detected in workplace drug screening programs.

Patients who are prescribed the prescription medication dronabinol for chemotherapy-induced nausea or HIV wasting syndrome will test positive for THC. Urine screening may be ordered to ensure that the medication is being taken by the patient and not sold illegally. It is possible to differentiate smoked marijuana from ingested dronabinol on urine drug testing.

Treatment — Acute intoxication with marijuana alone rarely requires medical treatment, although dysphoria may result in distress that causes the user to seek help. First-time users, older persons, users of high-potency marijuana, or those predisposed to psychiatric illness are at higher risk of experiencing unpleasant effects during intoxication.

Unpleasant effects of acute intoxication, such as anxiety, paranoia, or palpitations, are managed with supportive treatment. Placing the distraught user in a quiet environment and maintaining gentle contact is often sufficient until the acute effects subside; more severe paranoia or psychosis may require close observation with possible administration of a benzodiazepine or haloperidol for sedation.