CHRONIC USE — Signs of chronic marijuana use include reduction in activities and relationships not associated with the drug, and impairment in cognitive skills.

Withdrawal — Physical dependence on marijuana definitely occurs, and heavy use for more than 21 days results in a withdrawal syndrome after abrupt cessation. A significant proportion of marijuana users experience dependence symptoms, including tolerance and withdrawal (8 percent of low-frequency users compared with 46 percent of high-frequency users).

Marijuana withdrawal begins within ten hours of the last dose and consists of irritability, agitation, depression, insomnia, nausea, anorexia, and tremor. Most symptoms peak in 48 hours and last for five to seven days. Some symptoms, such as unusual dreams and irritability, can persist for weeks.

Marijuana withdrawal is uncomfortable but not life-threatening. Thus, treatment is entirely supportive and nearly always accomplished without the need for adjunctive medications.

Chronic health problems — Chronic marijuana use may result in multiple health problems. Marijuana is not smoked with filters, unlike most tobacco cigarettes. The amount of particulate matter that irritates the mucous membrane lining of the upper airway and enters the lungs is increased compared to tobacco smoking. Marijuana smoke contains nearly four times as much tar and 50 percent more carcinogens than tobacco.

Marijuana users are five times more likely to smoke tobacco cigarettes than non-users. Nicotine use can enhance some of the physiologic and psychologic effects of marijuana. Additionally, concurrent use of nicotine and marijuana likely enhance the deleterious health effects of each used independently.

It remains controversial whether marijuana increases mortality. Many adults who smoked marijuana when they were younger stop the behavior as they age. Thus, the duration of exposure seen with cigarette smoking is most often greater than with marijuana, which may result in less attributable mortality in people who smoke marijuana than tobacco cigarettes.