Levaquin
Treating bacterial infections has been close to the hearts of sailors, businessmen and dad for years. Knowing this, the medical world wouldn't stop at just penicillin, it had to go out and create many drugs, such as Levaquin, to help battle the nasty souvenirs we get from rusty nails and drunken whores in foreign ports.
It can turn you into a vampire.
Seriously. We mean, it can't make you immortal or bloodthirsty, but it can kill your ability to handle sunlight. It's called "phototoxicity," which is characterized by rapid, second-degree sunburns. So, basically a poor man's vampirism.
Alli
Alli is a weight-loss medication that prevents fat absorption. When you eat fat, the medication stops you from digesting it and helps it pass right along through.
According to their website, Alli calls these "treatment effects." Which implies that these effects can happen to pretty much everybody under the right circumstances. It's nothing major, mind you, just things like "gas with oily spotting." This would be a polite way of describing a fart that spackles your chair with a greasy stain of ass buckshot. In some cultures that's a great compliment for the host.
Of course, that's not all. Prominently displayed on their list of treatment effects are also "loose stools" and "more frequent stools that may be hard to control." Again, this should not be that alarming as these events are quite humorous when portrayed in the realm of slapstick comedy.