Marijuana use at 2-10 puffs, one to 16 times per day caused reduced pain and improved sleep in a survey of 15 patients with chronic pain who smoked cannabis for therapeutic purposes. Only 8 out of 15 reported experiencing a high. Side effects included drowsiness and loss of coordination.
A 2001 study showed that a lifetime of marijuana smoking was not associated with deficits in general intellectual function, abstraction ability, sustained attention, verbal fluency or ability to learn and recall new verbal and visuospatial
information after one month of abstinence. This was a controlled study of 180 volunteers including 63 heavy marijuana users (smoked cannabis at least 5000 times in their lives) who were smoking daily at study entry, 45 former heavy
users (smoked no more than 12 times in the previous three months) and 72 control subjects who had smoked no more than 50 times in their lives. Recall of word lists was reduced in heavy users who smoked daily at entry into the
study only during the first week of abstinence.
Any negative effect on IQ as a result of marijuana use may be temporary, as seen in the following study. Current smoking of five or more marijuana joints per week (assessed by self-reporting and urinalysis) was associated with reduced global IQ scores in a study of 70 subjects 17-20 years old. A negative effect was not observed among subjects who had previously been heavy users but were no longer using marijuana.
Marijuana smoking was, however, associated with an increased risk of depression in a study of 1920 people with no symptoms of depression at the onset of the study who were reassessed approximately 15 years after baseline data was
collected.
In addition, marijuana use was associated with an increased risk of psychosis in normal people, and a poor prognosis in patients with psychosis, in a study of 4,045 psychosis-free people and 59 patients with psychosis followed for a three year period.
Withdrawal symptoms (marijuana craving, decreased appetite, sleep difficulty and weight loss) did occur in an assessment of 12 marijuana smokers on 16 consecutive days during which they smoked marijuana as usual (days 1-5), abstained from smoking marijuana (days 6-8), returned to smoking marijuana (days 9-13), and again abstained from smoking marijuana (days 14-16). Aggression, anger, irritability, restlessness, and strange dreams increased significantly only during one of the abstinence phases.
According to the British Lung Foundation in a 2002 statement, smoking 3 to 4 marijuana cigarettes a day causes airway damage similar to smoking 20 or more tobacco cigarettes a day. Marijuana is smoked in a way that increases the respiratory burden of carbon monoxide and smoke particulates compared to smoking a similar quantity of tobacco. There is a possible link between cannabis smoking and emphysema.