Bloodletting
It was found that only in very few cases, this treatment helps cure a disease. The practice has now been abandoned for all except a few very specific conditions. There was no other treatment for hypertension. Bloodletting could sometimes have had a beneficial effect in temporarily reducing blood pressure by reducing blood volume. The problem with hypertension is that it is difficult to diagonse from its symptoms. Modern methods directly measure blood pressure. In Antiquity, this  effect was therefore unintentional. In most cases, the historical use of bloodletting was harmful to patients.