Cannabis consumption refers to the variety of ways cannabis is consumed, among which inhalation and ingestion are most common. All consumption methods involve heating the plant's THCA to decarboxylate it into THC, either at the time of consumption or during preparation. Salves and absorption through the skin (transdermal) are increasingly common in medical uses, both of CBD, THC, and other cannabinoids. Each method leads to subtly different psychoactive effects due to the THC and other chemicals being activated, and then consumed through different administration routes. It is generally considered that smoking, which includes combustion toxins, comes on quickly but lasts for a short period of time, while eating delays the onset of effect but the duration of effect is typically longer. In a 2007 ScienceDaily report of research conducted at the University of California–San Francisco, researchers reported that vaporizer users experience the same biological effect, but without the toxins associated with smoking. Δ9-THC is the primary component when inhaled, but when eaten the liver converts this to the more psychoactive 11-hydroxy-THC form.