Both the inhalation of marijuana smoke and the ingestion of THC reliably produces an increase in heart rate of 20 per cent to 50 per cent over baseline (Huber et al, 1988; Jones, 1984). When cannabis is smoked, the heart rate increases within two to three minutes, peaks within 15 to 30 minutes, and may remain elevated for up to two hours. When ingested, these effects are delayed for several hours, and last for four to five hours (Maykut, 1984). There are also complex changes in blood pressure which depend upon posture: blood pressure is increased while the person is sitting or lying, but decreases on standing, so that a sudden change from a recumbent to an upright position may produce postural hypotension and, in extreme cases, fainting

Orthostatic hypotension (also known as postural hypotension, orthostatic intolerance and, colloquially, as head rush or a dizzy spell) is a sudden fall in blood pressure, typically greater than 20/10 mm Hg, that occurs when a person assumes a standing position, usually after a prolonged period of rest.

Symptoms, which generally occur after sudden standing, include dizziness, lightheadedness, headache, blurred or dimmed vision (possibly to the point of momentary blindness), and fainting. They are consequences of insufficient blood pressure and cerebral perfusion (blood supply).