One of the most common adverse effects of cannabis is sinus tachycardia which can last for several hours. Sometimes users complain of palpitations. Heart rate is typically increased by 20-50% depending upon individual circumstances. The exact mechanism is not clear, but the effect is antagonised by the beta-adrenergic blocker, propranolol. Cannabis causes release of adrenaline, has antimuscarinic properties and can increase peripheral blood flow. Tachycardia could be mediated by these mechanisms acting in concert—all of them involve the adrenergic system. Tolerance to tachycardia does occur to some extent after chronic use, but the response is never completely lost. There are remarkably few reports of cannabis-induced arrhythmias, although premature ventricular beats are occasionally observed.
Tachycardia could be harmful to those suffering from cardiac disorders such as angina or heart failure. Two studies have assessed the effects of cannabis smoking on the exercise tolerance of patients with angina (Aronow and Cassidy, 1974; Aronow and Cassidy, 1975). Both concluded that cannabis cigarettes decreased the amount of exercise needed to trigger anginal attacks by an average of 50%. By comparison, placebo cigarettes reduced exercise tolerance by only 9%, and high nicotine content cigarettes by 23%.
Acute cardiac toxicity has been described very rarely. There are a very small number of cases of myocardial infarction attributed to cannabis in the medical literature (Collins et al., 1985; Macinnes and Miller, 1984). However, infarction and cannabis smoking are both common, and their occurrence in the same person at the same time is probably no more than coincidence. Usually cannabis falls suspect because the patient experiencing infarction is younger than average, and investigators then begin to look for a cause.
Orthostatic hypotension is a well-known adverse effect of cannabis. It has been suggested that this occurs when cannabinoids bind to the peripheral cannabinoid receptor (CB1) and inhibit sympathetic tone (Varga et al., 1995). Sometimes the hypotensive effect is dramatic enough to cause syncope (Merritt et al, 1982). High doses produce a reddening of the eyes due to vasodilation. Facial flushing is also a known effect.
However, the dizziness reported by many cannabis users when standing upright after smoking cannabis may not be entirely due to hypotension. A study of ten young men revealed that reduced middle cerebral artery blood velocity could be identified in all subjects who reported moderate to severe dizziness after smoking cannabis and standing upright. Only those with the most severe dizziness also showed reduced blood pressure. The authors suggested that impaired cerebral autoregulation of bloodflow was important in causing dizziness (Mathew et al., 1992).
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Among the evils which a vitiated appetite has fastened upon mankind, those that arise from the use of Tobacco hold a prominent place, and call loudly for reform. We pity the poor Chinese, who stupifies body and mind with opium, and the wretched Hindoo, who is under a similar slavery to his favorite plant, the Betel but we present the humiliating spectacle of an enlightened and christian nation, wasting annually more than twenty-five millions of dollars, and destroying the health and the lives of thousands, by a practice not at all less degrading than that of the Chinese or Hindoo.