The bioavailability of THC, i.e. the amount of THC in a given dose that makes it to general circulation, varies dramatically depending on the method of delivery. When THC is delivered intraveneously (a bioavailability of 100%), it produces effects at only 0.06mg/kg (Ohlsson et al, 1980). Intravenous doses of 5mg can produce peak plasma concentrations of greater than 400 µg/L (Kelley and Jones, 1992). The amount of THC in a cigarette is typically between about 10 and 100mg of THC. A single, high potency (10% THC by weight) cannabis cigarette weighing one gram contains 100mg of THC. Half or more of this THC is lost in sidestream smoke that is never delivered to the lungs (Perez-Reyes, 1990). Experiments using a smoking machine show that depending on puff volume and puff interval, as little as 16-19% of the THC present in the cigarette may be delivered as mainstream smoke, while as much as 69% is transferred to mainstream smoke if the cigarette is smoked in a single puff with no loss via sidestream smoke (Davis et al, 1984). About 30% of THC is assumed to be destroyed by pyrolysis. More THC is lost due to incomplete absorption of inhaled doses in the lungs. Actual bioavailability via a cigarette, i.e. the percentage of THC in the cigarette that is delivered to general circulation, ranges from 10 to 35%, and varies according to puff volume, breathhold duration, and depth of inhalation (Grotenhermen, p. 331). More experienced users tend to achieve higher levels. This appears to be due to different smoking behaviors in experienced users, since plasma levels and AUC values are about the same for heavy and light users following intravenous THC administration (Ohlsson et al, 1982). Bioavailability is higher (45% in one case) with pipes, which reduces loss via sidestream smoke (Agurell and Leander, 1971).