See this site for explanations regarding those stats: Drug War Distortions: Emergency Room Visits

The federal DAWN report itself notes that reports of marijuana do not mean people are going to the hospital for a marijuana overdose, it only means that people going to the hospital for a drug overdose mention marijuana as a drug they use. Since marijuana is the most widely used illegal drug it is the most mentioned illicit drug when people come to the hospital for any reason. Also, alcohol-in-combination is a larger problem than any of the illicit drugs.....................Important Note: Mention of a drug in an emergency department visits does not mean that the drug was the *cause* of the visit. The DAWN report for 2000 says, regarding mentions of marijuana/hashish.......................Since marijuana/hashish is frequently reported in combination with other drugs, the reason for the ED contact may be more relevant to the other drug(s) involved in the episode."
Drug War Distortions: Emergency Room Visits