I. Marihuana is the Latin-American name for a cigarette preparation of the hemp plant. The active principle is cannabis sativa: the drug has various synonyms—hasheesh, ganja, reefers, Indian hemp, etc. It has been used for centuries in the Orient and later in Latin America. Mental states produced by the drug constitute a fairly definite clinical entity.II. A study of the relation between violent crime (murder, assault, rape, etc.) with marihuana showed no direct correlation. It is clear from this study, that in this region the drug is a "breeder of crime" only when used by psychopathic types in whom the drug allows the emergence of aggressive, sexual or anti-social tendencies. The addiction to marihuana is not on the same deep physiological or psychologic level that morphine addiction is.III. The clinical pictures observed can be divided into three groups:(1) Acute intoxications.(2) Emotional reactions to the intoxication features.(3) Toxic psychosis due to admixture of drug effects and basic psychosis (manic-depressive, schizophrenic, etc.).IV. Psychologic factors are of great importance in the emotional reaction of an intoxication, bringing various personality forces and conflicts to the surface.V. The psychologic and physiologic effects of cannabis intoxication have been well studied. They are:(1) A change in time perception, reality feeling, somatic, sensory and motor phenomena.(2) Disturbance of consciousness with difficulty in memory retention.(3) Change in subjective evaluation of perception of visual, tactile, proprioceptive, auditory experiences because of disintegration of sensation to a primitive level of perception. The result of this change in body-model (Körperschema) perception may be expressed in feelings of unreality that appear as panic-states in narcissistic or hysterical individuals.(4) A mood reaction consisting of elevation with periods of sudden boisterous laughter.(5) A primary stimulus to the impulsive life with direct expression in the motor field.