The use of leeches for medicinal purposes dates back at least 2,000 years. This practice peaked in the 18th and 19th centuries when practitioners employed the parasites to treat pathologies including gout, headaches, mental illness, obesity, and whooping cough among others. Leech therapy rapidly declined by the beginning of the 20th century when the intervention was found to have little recognizable benefit.

More recently, however, modern medicine has seen a resurgence in the application of leeches. Surgeons now commonly use the parasites to treat acute venous congestion after free-tissue transfer or replantation. This microvascular complication stems from inadequate venous drainage from the tissue in question. Quite literally, blood backs up and compromises arterial inflow, which leads to hypoxia and ultimately to surgical flap demise. Signs of acute venous congestion include dusky or bluish-purple discoloration, edema, brisk capillary refill, and relative tissue warmth.