CHAPTER 2-98: MARIJUANA

INTRODUCTION

Marijuana consists of the leaves and flowering parts of the plant Cannabis sativa. It usually is smoked in cigarettes ("joints" or "reefers") or pipes or added to food (usually cookies, brownies, or tea). Resin from the plant may be dried and compressed into blocks called hashish. Marijuana contains a number of cannabinoids; the primary psychoactive one is delta-9-tetrahydrocannabinol (THC). THC is available by prescription in capsule form (dronabinol [Marinol]) and is available in liquid form for inhalation using electronic cigarette devices. Marijuana can also be inhaled using a vaporizer (such as Volcano), which vaporizes THC without combusting marijuana. THC is used medically as an appetite stimulant for patients with such conditions as AIDS-related anorexia; it also is used as treatment for vomiting associated with cancer chemotherapy, for chronic pain, and for multiple sclerosis, glaucoma, and other disorders. In some US states cannabis products are legal for medical use, and in others for recreational use.

Synthetic cannabinoid analogs such as JWH-018 and many similar compounds, sold as "K2" or "Spice" and in some so-called "herbal" preparations, are banned in some states but available via the Internet. These may produce acute toxicity similar to that seen with THC; some have been associated with seizures.

Cannabinoid antagonists include rimonabant (a CB₁ selective antagonist) which was developed as medication to reduce appetite and weight, and also for smoking cessation. It was marketed briefly in Europe and then withdrawn due to psychiatric side effects, particularly depression and suicidal ideation.

MECHANISM OF TOXICITY

1. THC, which binds to cannabinoid (anandamide) CB₁ and CB₂ receptors in the brain, may have stimulant, sedative, or hallucinogenic actions, depending on the dose and time after consumption. Both catecholamine release (resulting in tachycardia) and inhibition of sympathetic reflexes (resulting in orthostatic hypotension) may be observed.

2. Pharmacokinetics. Only about 10–20% of ingested THC is absorbed into the bloodstream, with onset of effects within 30–60 minutes and peak absorption at 2–4 hours. It is metabolized by hydroxylation to active and inactive metabolites. Blood THC levels decline rapidly after inhalation due to tissue redistribution, followed by an elimination half-life of 20–30 hours, which may be longer in chronic users.

TOXIC DOSE

Typical marijuana cigarettes contain 1–4% THC, but more potent varieties may contain up to 25% THC. Hashish contains 3–6% and hashish oil 30–50% THC. Dronabinol is available in 2.5-, 5-, and 10-mg capsules. Toxicity is dose related, but there is much individual variability, influenced in part by prior experience and degree of tolerance.

CLINICAL PRESENTATION

1. Subjective effects after smoking a marijuana cigarette include euphoria, palpitations, heightened sensory awareness, and altered time perception, followed after about 30 minutes by sedation. More severe intoxication may result in anxiety, impaired short-term memory, depersonalization, visual hallucinations, and acute paranoid psychosis. Cannabis use may precipitate or exacerbate ...