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TABLE 1.4 Primary Symptoms of 43 Individuals Who Reported to IOM Study Team
	Symptom Frequency		Multiple Symptoms
				No. Who
				Reported	%/ of Those
		'', of Total		(primary)	Who Reported
Primary	No. of	Symptoms		Additional	Primary
Symptom	Reportsa	Reported		Symptoms	Symptoms
Anorexia, nausea,
vomiting	21	31		13	62
Diarrhea	4	6		3	75
Intraocular pressure	2	3		1	50
Mood disorders	12	18		7	58
Muscle spasticity	12	18		7	58
Pain	16	24		13	81
Total	67			44	66
aForty-three persons reporting; 20 reported relief from more than one symptom.

The variety of stories presented left the study team with a clear view of people's beliefs about how marijuana had helped them. But this collection of anecdotal data, although useful, is limited. We heard many positive stories but no stories from people who had tried marijuana but found it ineffective. This is a fraction with an unknown denominator. For the numerator we have a sample of positive responses; for the denominator we have no idea of the total number of people who have tried marijuana for medical purposes. Hence, it is impossible to estimate the clinical value of marijuana or cannabinoids in the general population based on anecdotal reports. Marijuana clearly seems to relieve some symptoms for some people—even if only as a placebo effect. But what is the balance of harmful and beneficial effects? That is the essential medical question that can be answered only by careful analysis of data collected under controlled conditions.

Cannabis and the Cannabinoids

Marijuana is the common name for Cannabis sativa, a hemp plant that grows throughout temperate and tropical climates. The most recent review of the constituents of marijuana lists 66 cannabinoids (Table 1.5).16 But that does not mean there are 66 different cannabinoid effects or interactions. Most of the cannabinoids are closely related; they fall into only 10