SINCE 1972, AN ACCUMULATING BODY OF MEDICAL EVIDENCE SHOWS THAT MARIJUANA HARMS ITS USERS. EVIDENCE SHOWS THAT WITH CASUAL CONSUMPTION, THERE IS A POSSIBILITY OF A TRANSIENT PSYCHOSIS INVOLVING INTENSE ANXIETY, PANIC, AND DEPRESSION. LONG-TERM EFFECTS INCLUDE MENTAL CONFUSION, POOR CONCENTRATION, AND DIFFICULTY IN CONCEPT FORMATION AND RECENT MEMORY. SIGNIFICANT EVIDENCE EXISTS THAT PROLONGED USE CAN PRODUCE ORGANIC AND PERMANENT BRAIN DAMAGE. ANIMAL STUDIES SHOW THAT THE INTAKE OF LESS THAN TWO MARIJUANA CIGARETTES A WEEK (EQUIVALENT DOSAGE FOR HUMANS) FOR 3 MONTHS CAUSES SERIOUS, AND QUITE POSSIBLY PERMANENT, ALTERATION OF BRAIN FUNCTIONS. THE INHALATION OF CANNABIS SMOKE DAMAGES HUMAN LUNG TISSUE, PRODUCING SINUSITIS, PHARYNGITIS, BRONCHITIS, AND EMPHYSEMA IN A MUCH SHORTER TIME THAN WITH TOBACCO USE. THERE IS ALSO EVIDENCE THAT THE TETRAHYDROCANNABINOL (THC) COMPONENT OF CANNABIS REDUCES THE BODY'S CAPACITY TO RESIST INFECTIOUS DISEASES. PROVISIONAL FINDINGS INDICATE THAT CANNABIS MAY CAUSE DISRUPTION OF SPERM PRODUCTION, IMPOTENCE, AND A REDUCED LEVEL OF TESTOSTERONE. GIVEN THE WIDESPREAD USE OF MARIJUANA, PARTICULARLY AMONG THE YOUNG, IT CONSTITUTES A SERIOUS HEALTH HAZARD, AS WELL AS A THREAT TO THE SOCIAL FABRIC OF A SOCIETY WHERE USE IS CHRONIC. ARGUMENTS FOR ITS DECRIMINALIZATION ARE MYTHS WHICH FAIL TO DEAL WITH THE EVIDENCE OF ITS HARMFUL EFFECTS. ALTHOUGH MARIJUANA LAWS WILL INEVITABLY BE BROKEN, SUCH LAWS DO NONETHELESS EXERT A RESTRAINING INFLUENCE ON LEVELS OF USE. BECAUSE OF THE HEALTH THREATS INVOLVED, IT IS CRITICAL THAT LEGAL SANCTIONS AGAINST CANNIBIS USE BE MAINTAINED. APPENDIXES COMPARE THE DIFFERENCES IN EFFECTS UPON USERS BETWEEN ALCOHOL, TOBACCO, AND CANNABIS. FOOTNOTES ARE PROVIDED. (RCB)