The epidemic diseases that devastated the New World - measles, smallpox, tuberculosis, influenza, etc - were "crossovers" that had jumped the species barrier from Old World livestock.

Europeans, Africans, and Asians had thousands of years of natural selection for immunity, so even though these disease are still serious, the majority of Old Worlders could shake them off. However, New Worlders had no previous exposure, and suffered 99% fatalities upon first encounter (which is probably what happened back in the Old World too, back before recorded history when the microbes first crossed over into mankind.)

Due to accident of history/biology/geology, there weren't many easily domesticable animals in the New World. Llamas and Alpacas in the mountains of South America, turkeys in Mexico, and that's about it. (Indians had dogs, too, but DNA shows that they brought their dogs from Asia long ago, they weren't separately domesticated here.)

Hence, we had LOT of diseases to give to them, and they only had a few to give to us. (Syphilis is almost certainly a new world disease.)

Drug wise, the damage was more equal. We had alcohol, Indians had tobacco. Both were enshrined in ritual and subject to social controls in their original cultural context. Then when the 2 cultures met, and switched drugs, removing them from their traditional cultural controls, the Indians became alcoholics and the white men got lung cancer...