Bloodletting (הקזת דם) was a commonplace medical procedure in the Mishnaic times (see Shabbos 129). It is widely accepted that the ancient healers believed that:
"... many diseases were caused by plethoras, or overabundances, in the blood... "Bleeding" a patient to health was modeled on the process of menstruation. Hippocrates believed that menstruation functioned to "purge women of bad humors". During the Roman Empire, the Greek physician Galen, who subscribed to the teachings of Hippocrates, advocated physician-initiated bloodletting... The Talmud recommended a specific day of the week and days of the month for bloodletting... (WIKI ibid)"
Rambam started to treat the bloodletting with more caution (Deos 4,14):
"לא ירגיל אדם עצמו להקיז דם תמיד, ולא יקיז דם אלא אם היה צריך לו ביותר; ...".
We also know that hurting oneself is a transgression, and today the bloodletting would be forbidden after proven seriously wrong. The Sages themselves saw a great danger in it.
I wonder if the Sages' practice of bloodletting was based purely on the medical customs of the leading "scientists" of their times, or had some Jewish traditional roots?
Please notice, this question is not about the benefits/dangers of bloodletting, but about its origin.