James Morrison was a doctor in the 19th Century who thought he could cure just about everything by making people have unstoppable diarrhea.
In the 1800s, medicine wasn't exactly as developed as you'd like it to be, from a modern perspective. For example, you could still find many a doctor whose response to you losing blood would be "QUICK, TAKE MORE OF THIS MAN'S BLOOD, WE'RE LOSING HIM". In this environment, with distrust of the medical profession quite high, there was room for a lot of quacks, and James Morrison very much made himself at home in this space.
Morrison had the idea that all diseases were caused by the impurity of the blood, for which the solution was profuse defecation. His initial belief came from the fact that he was able to cure his own life-long constipation by creating his own home-brew laxatives. For some reason, he extrapolated from this that making people poop more easily would cure people with things like aneurisms or smallpox.
The scientific method would have told him that giving people diarrhea wouldn't cure them of (genuine example he thought his pills could cure) diarrhea. However, James Morrison was no scientist, and he felt he didn't need any more proof than a "just trust me ok". Unfortunately, many desperate patients felt the same.
Morrison created his own brand of vegetable pills to help people defecate. The Universal Vegetable Pills were marketed as being able to cure everything. One advert, for instance, shows a man who no longer needs his crutches, having apparently gone to the toilet so well he had regrown his amputated legs.
While the advert didn't go into the specifics (did he poop out a leg??), it's very clearly intended to imply it would restore the limbs of amputees, a promise it sure as heckfire could not live up to.
"When I awakes in the morning to kick off the clothes," the man in the advert exclaims, "I'm blessed if I didn't find myself with these 'ere couple of jolly good legs and my old wooden ones right at the bottom of the bed!!!"
The doctor, you'll be shocked to learn, wasn't too fussed about figuring out things like dosage, and here's where things got dangerous. As far as he was concerned, if you fancied ramming down dozens of the laxatives that was fine. He even recommended that you take laxatives for the diarrhea, "so as effectually to carry off the morbid humours", as well as dysentery. Needless to say, but this is like someone trying to treat your ball pain with successive blows to the testicles. He advised that you were likely to feel worse before you get better, and to not let that stop you from taking his extremely profitable medicine.
Morrison miraculously managed to keep away from the blame, with lower down drug vendors being jailed for manslaughter instead of him. In 1836, one agent was jailed for manslaughter after a 32-year-old who was suffering from mild knee pain was given 1,000 over 20 days, and effectively pooped himself to death, for an injury he could have walked off. Accusations of manslaughter kept rolling in, but Morrison always managed to escape while the lower-level pushers were jailed.
With the deaths piling up, however, other medical professionals began to campaign against the quack, but they were fairly ineffective at slowing down his sales. This may be because the adverts tended to depict people being turned into vegetation by the vegetable pills, rather than simply telling people "these pills will make you poop yourself to death" in large font.
While it might be nice to see the doctors railing against Morrison as heroic, a lot of them still believed in practices like bloodletting, and in their advertising campaign against him used some fairly awful racist cartoons.
Morrison eventually died in 1840 as a very rich and unprosecuted man, before his sons took over the business and went on to make a lot more money from his quackery.