The Food and Drug Administration (FDA) has cleared the commercial marketing of leeches for medicinal purposes for the first time ever.
The medicinal leech has a long history of use in medicine, although today its use is mainly limited to limb reattachment procedures instead of the wide-ranging medical use of the past. Leeches were once so commonly used that doctors were popularly called leeches. In Old High German, lâhhi (etymon of leech) means "physician".
Leech saliva contains a number of compounds which assist in its feeding. An anaesthetic limits the sensations felt by the host (and thus reduce the chance of the host trying to detach the leech). A vasodilator causes the blood vessels near the leech to become dilated, and thus provide the leech with a better food supply.
Lastly, the leech saliva contains a complex protein called hirudin, which is a highly effective anticoagulant. The leech needs this to prevent blood clots (which would block its feeding) from forming in the wound created by its mouthparts. These properties are difficult to achieve using other medical techniques, and it is for this reason that leeches have come back into clinical practise in the last 25 years. The small amounts of hirundin present in leeches makes it unsuitable to be harvested for more general medical use, so hirudin (or related chemicals) have been synthesised using recombinant-DNA technology.
Bdellatomy is the practice of cutting the leech open slightly while it is sucking blood to let the blood in it out, so thinking that it is not full yet, the leech continues to bite instead of detach itself. This practise was first recorded in 1868 by Daily News.