Which method of healing involved intentionally letting blood out of the body?

The method of healing that involved intentionally letting blood out of the body is bloodletting. This practice dates back to ancient times and was based on the belief that many illnesses were caused by an imbalance of bodily humors, specifically blood. By removing blood, healers aimed to restore this balance and promote health. Bloodletting was often performed using various tools such as lancets or leeches and was thought to alleviate conditions ranging from fevers to chronic diseases.

The other methods listed serve different purposes: acupuncture involves inserting needles into specific points on the body to alleviate pain and promote healing, cupping uses suction to improve circulation and relieve muscle tension, while trepanation is the surgical practice of drilling holes into the skull to treat head injuries or pressures within the skull. Each of these practices reflects different historical understandings of medicine and anatomy, but they do not involve the direct drainage of blood as bloodletting does.