1. Scab snorting
Practised in India and China, this 17th-century inoculation technique consisted of inhaling powdered scabs from smallpox sufferers. Weird as it sounds, it did provide some immunity.
For 2,000 years, doctors bled patients to purge them of diseases, often with leeches. This long-running (and highly ineffective) tradition was only discredited in the 1900s.
The treatment for syphilis for centuries was mercury, a very toxic metal. With debilitating side-effects of its own, it did little more than hasten the deaths of its patients.
5. Tortoise brain
Ancient Egyptians developed some effective cures, but their treatment for cataracts was not one. It involved smearing tortoise brains mixed with honey over the eyes.