Leech therapy has been around for over 2,000 years, evolving from a go-to remedy for nearly every ailment to a scientifically validated tool in modern medicine. At the height of their popularity in 19th-century Europe, millions of leeches were harvested annually — France alone imported 33 million a year — fueling a booming transnational trade. French physician François-Joseph-Victor Broussais was a major driver, prescribing leeches to treat everything from typhus to dysentery. But their overuse during the cholera epidemic of the 1830s, combined with dwindling wild populations, led to a sharp decline in their medical use by the end of the 19th century.

Their modern revival came in 1985, when American plastic surgeon Joseph Upton used leeches to successfully save a reimplanted ear in a 5-year-old boy. The FDA formally approved leeches as a medical device for reconstructive and plastic surgery in 2004. Today, they're also being explored for osteoarthritis, venous disorders, and chronic pain, and remain part of Arabic, Ayurvedic, and East Asian traditional medicine.

Quick Facts:

• Leeches share a symbiotic relationship with Pseudomonas hirudinis, a bacterium that helps digest ingested blood
• Leeches are now protected by law in Germany and several other European countries
• A mechanical bloodletting device was developed in 1817 as an early alternative to leeches

Why it matters: Leech therapy's journey from ancient remedy to FDA-approved medical device is a reminder that some traditional treatments can withstand scientific scrutiny — and that medicine's history is rarely a straight line.