Every medicine is poison. Every type of general anesthesia is poison. Every had surgery under general anesthesia? You took poison. But you are in the larger group of folks who didn't react negatively.
Penicillin was a wonder drug when discovered, saved (still saves) a lot of lives back then. Some humans, though, are highly allergic to it, have died after taking it. Every medication has a risk.
Newer treatments (immunotherapy) for some vicious cancers (sarcoma, for example) are still in clinical trial. Highly, highly expensive, so much so that nobody can afford them. They offer possible success, but at the same time they can turn the immune system against the patient and death may ensue quickly. Patients (or parents of child) are warned of this possiblity, but in those desperate situations many will opt for treatment if approved (by medical boards). Former pres Jimmy Carter had sarcoma in his brain while in his 90s (he still is). He took immunotherapy and achieved a cure. My 20 year old nephew was found to have same type of sarcoma filling his lungs (first ever chest x-ray, he had a mild cough, senior in college). He went to one of the cancer centers, got approved for the same type treatments as Jimmy Carter. He/parents opted in for it. Didn't help. At another center a different but same category treatment was offered, he took it. Seemed to improve for a short time, then he crashed and burned (awful term but you get it). The parents have no regrets for trying the treatments, since otherwise he had NO chance. Did the treatment do him in or the disease? You guys would say if Trump was around that Trump killed my nephew. Which of course would be majorly silly.