Cannabis has been used since pre-historic times for its special acute effects termed as “The Cannabis High”. Here the acute effects of Cannabis are discussed with detail.

ACTIVE CHEMICALS IN CANNABIS:

      Cannabis plant secretes more than 400 chemicals but it is famous for its terpeno-phenolic group of chemicals called as cannabinoids e.g. cannabinol, cannabidiol, cannabinolidic acids, cannabigerol, cannabichromene, and several isomers of tetrahydrocannabinol (THC). Most important is the isomer Δ ⁹-THC which is responsible for the spectrum of effects of Cannabis. The effects of Cannabis are diverse and thus do not allow classification as hallucinogen, stimulant, sedative or tranquilizer. Dronabinol is the synthetic THC.

THRESHOLD DOSES

        Threshold dose depends upon the route of administration and the potency (%THC per dry weight of material) of Cannabis used.  

·        Intravenous route gives 100% bioavailability and sudden peak in plasma Cannabis level.

·        Smoking results in rapid absorption and plasma level peaks even prior to end of smoking. This also falls rapidly to <5ng/ml in 3 hours.

·        Ingestion of Cannabis may lead to slower plasma peaks and low bioavailability.

Table: Comparison of the effectiveness of THC application to man via relevant routes

MODE OF ACTION

          The binding of THC to cannabinoid receptors (CB1 & 2) leads to pharmacological effects of Cannabis. CBs are receptors for natural endo-cannabinoids made by body. THC is a partial agonist at CB i.e. increases its working but not 100%. CB1 is concentrated in brain while CB2 is found in periphery on immune system cells. Activation of CB precipitates release of dopamine (the mood elevator). THC also activates the opioid receptors through unknown mechanisms, also causing dopamine release. This justifies the spectrum of effects related with Cannabis use.

CANNABIS-PSYCHOLOGICAL EFFECTS

          Highest concentration of THC receptors are in area controlling pleasure, memory, thoughts, concentration, sensory and time perception, and coordinated movement. Correspondingly, these are areas affected during Cannabis high.

Thus at recreational doses:

1. During the Cannabis ‘high’ people feel relaxed, talkative, euphoric, giggly, relaxed inhibitions, having pleasurable sensations with altered state of consciousness and disorientation. Some also feel more philosophical, aware, or enlightened.
2. Cannabis hinders short-term memory thus causing troubles in handling cmplex tasks (at lower doses), and even simpler tasks (at higher doses).
3. Cannabis changes the way in which sensory information gets into and is processed by the hippocampus, a brain component that is crucial for learning, memory, and the integration of senses with emotions. Learned behaviors also deteriorate.
4. Because of the its effects on perceptions and reaction time, Cannabis users could be involved in auto crashes.
5. Cannabis users also may become involved in risky sexual behavior.
6. Students may find it difficult to concentrate on studies after Cannabis use.
7. Athletes could find their performance off with timing, movement and coordination all affected.
8. There is a more vivid sense of smell, taste, sight and hearing.

  Large doses of Cannabis, especially when ingested, can cause "toxic psychosis." Symptoms include auditory and visual hallucinations, paranoid delusions, fluctuating emotions, flights of fragmentary thoughts with disturbed associations, a dulling of attention despite an illusion of heightened insight, image distortion, confusion and amnesia.

     These symptoms are dose dependant and temporary and fade away after use of Cannabis is discontinued.

CANNABIS-PHYSIOLOGICAL EFFECTS

     The most frequent immediate effects with Cannabis use include increased heart rate, reddening of the eyes, dry mouth and throat, increased appetite, vasodilatation, some loss of coordination and poor sense of balance. 

    One study found that risk of heart attack more than quadruples in the first hour after smoking Cannabis which might occur from Cannabis’s effects on blood pressure and heart rate (it increases both) and reduced oxygen-carrying capacity of blood.

OTHER EFFECTS

Tolerance, Dependence and Withdrawal Effect: Tolerance may develop fast to some pharmacological effects of Cannabis after only a few doses, but also disappears rapidly

Interactions of Cannabis with other drugs: Cocaine and amphetamines may lead to increased blood pressure, heart rate and possible cardio toxicity. Benzodiazepines, barbiturates, ethanol, opioids, antihistamines, muscle relaxants and other CNS depressants increase drowsiness and CNS depression. When taken concurrently with alcohol, the effects are more pronounced than added up effects of both alcohol and Cannabis.

Unusual sensitivity: May occur in first time Cannabis users with more pronounced effects at lower doses, acute anxiety and paranoid thoughts. More likely at initial high doses of Cannabis.

DURATION AND HALF-LIFE

      Effects from smoking Cannabis start within minutes, peak in 10-30min, and the high lasts about 2 hours.  Most behavioral and physiological changes return to normal within 3-5 hours, but some residual effects last up to 24 hours. Psychomotor impairment can persist even after the high has dissipated.

AFTER EFFECTS

• When the early effects fade, over a few hours, the user can become very sleepy.
• Because of irritants in Cannabis smoke, there can be frequent cough and phlegm, colds and bronchitis.
• Persistent use may follow the initial recreational use of Cannabis, resulting in long term effects.

TESTS FOR CANNABIS

        There are urine and blood tests available for detecting Cannabis. Urine sample may be positive after 3-4 hours of use above the threshold levels and it will be sufficient to trigger a positive result for 2-4days. The plasma levels may show traces even up to 5 weeks after Cannabis use. The detection window could be longer in chronic and heavy users.