My comment was somewhat flippant and we were talking about "illicit" drugs and not prescribed or "approved" drugs - and drugs under medical supervision is usually fine, although, since you brought it up - paracetamol for example, because it is such an old drug detailed studies have largely not been done until recently. These studies have shown that paracetamol use is associated with increased rates rates of death, heart attack, stomach bleeding and kidney failure. Paracetamol is known to cause liver failure in overdose, but it also causes liver failure in people taking standard doses for pain relief. The risk is only about one in a million, but it is a risk. All these different risks stack up. So, as I said no drug is "safe" but also needed in a lot of cases, under medical supervision. Illicit drugs, not under the supervision of a medical professional is not safe, no.