The name Unani is derived from a Greek word Ionian which means medicine a symbol of life. Tibb means the knowledge of the states of the human body in health and illness (decline of health). Unani Tibb strives to find the best possible ways by which a person can lead a healthy life. Hence, Unani is an age old, time tested system of medicine dating back 5000 years to Greece. It refers to a tradition of Greeko-Arabic medicine which is based on the teachings of Greek physician Buqrat (Hippocrates; 460-377 BC) and Roman physician Jalinoos (Galen) and developed into an elaborate medical system by Arab and Persian physicians such as Al Razi (Rhazes), Avicenna (Ibne sina), Al Zahrawi and Ibn Nafis. Unani is a form of traditional medicine widely practised in South Asia and draws on the ancient traditional systems of medicine of China, Egypt, India, Iraq, Persia and Syria. It is still popular in many Arab and East Asian countries. In fact Unani medicine and herbal products are gradually more being used in many countries where modern medicine is easily available. India has accepted it as one of the alternative health care system and has given it an official status.

The use of leeches in medicine dates as far back as 3,500 years ago, when they were used for bloodletting in ancient Egypt. Leech therapy is one of the oldest medical practices, having been practiced among the diverse ancient people, including the Mesopotamians, the Egyptians, the Greeks, the Mayans and the Aztecs. In Greece, Leech therapy was first introduced by a famous Unani physician, Hippocrates, also known as father of medicine. The popularity of this therapy was reinforced by the ideas of Roman philosopher Galen, who classified Leech therapy as a method of treatment and prevention of health. He believed that blood was the dominant humour and the one in most need of control. In order to maintain the balance of humours, a physician would either remove excess blood from the body or advise them any other treatment for evacuation of morbid humours. When Islamic theories became known in the Latin speaking countries of Europe, Leech therapy became more widespread. Together with venesection, it was central to Arabic surgery, which is mentioned in classical Unani literature; “Alqanoon fil tib” and “Altasreef liman Ajeza Anittalif”. It was also known in Ayurvedic medicine, described in Sushruta samhita. Dhanvantari, the Indian god of Ayurveda holds a leech in one of his 04 hands. The practice of this therapy continued throughout the middle Ages but began to be questioned in the 16^thcentury, particularly in northern Europe.[7,11] In 1980, medicinal leech therapy got a big boost by plastic surgeons, who used leeches to relieve venous congestion especially after skin grafting in transplant surgery. This use of leech therapy provides a good example for its current status. When appendages are reattached following traumatic amputation, it is often possible to reconnect the larger arterial blood vessels, but not the thinner more delicate venous vessels. The body will eventually develop the necessary venous connections to drain the area of oxygen-depleted blood but if this does not occur rapidly enough, pooling of venous blood can produce enough swelling and pressure with which fresh arterial blood may no longer be able to enter the re-connected limb. In this situation, leeches are used to drain the local blood and decompress the pressure within the grated limb otherwise, a risk of necrosis develops as a complication.[12,13]

Leeches are carnivorous or blood sucking annelid worms with pronounced ability to extend or contract their bodies. They are hermaphrodite in nature and are distributed all over the world, except the polar zones, deserts and altitudes exceeding 3,700 m. In India, about 45 species belonging to 22 genera occur.[16] The common Indian species are Hirudinaria granulosa, H. viridis, H. javanica, and H. manillensis. These species are also common in Burma, Pakistan, Bangladesh and Sri Lanka. Haemadipsa is a land leech of the hills of Southern India.[17]

The legendary Unani scholar, Ibne Sina in his famous treatise “Canon of Medicine”, an encyclopedia of medicine which served as a standard text book of medicine in Europe till 17^th century A.D, has described the procedure of Leech therapy in a very comprehensive manner and narrated the following steps of the whole procedure:[1–3]

According to the Unani doctrine, leech therapy works on the principles of Tanqiyae Mawad (Evacuation of morbid humours) and Imalae Mawad (Diversion of humours). Tanqiyae Mawad means the resolution and excretion of morbid humors and excess fluids from the body, thereby maintaining the homeostasis in the quality and quantity of four body humors, which is actually responsible for the maintenance of normal health. Imalae Mawad refers to the diversion of the morbid fluids from the site of affected organ to the site where from it is easily expelled from the body tissues. Based on this holistic approach, Unani physicians have been widely using this therapeutic regimen for a number of diseases. The effectiveness of this therapy may also be attributed to the Mussakin (sedative) and Muhallil (anti-inflammatory) actions of saliva of leeches.[3,4,9]

In recent past years, various clinical as well as experimental studies have been conducted globally to evaluate the efficacy of leech therapy in various ailments using standardized outcome measures. The leeching has proved very beneficial in microsurgeries and different types of arthritis.[29] In a study conducted in Germany, the effectiveness of leech therapy in osteoarthritis of knee was established. The patients (n = 51) received a single sting of leeches (4 to 6 in number). The primary end point pain at 7^th day was reduced from 53.5±13.7 to 19.3±12.2 in leeching group compared to the control group where the pain was reduced from 51.5±16.8 to 42.4±19.7 with topical diclofenac application.[25] In another study, the hirudin was tested for thrombin inhibition in synovial inflammation in Antigen Induced Arthritis (AIA). The study was conducted on animal models where experiments showed hirudin did indeed significantly attenuate the severity of AIA as measured by both ^99mTC uptake and synovial histology. The intra-articular fibrin staining was reduced by hirudin treatment. There was a clear reduction seen in synovial inflammation by hirudin.[30] The hirudin as a potential therapeutic agent for arthritis has also been advocated by K Scott, Professor in University of Auckland, New Zealand[31] and synovial stimulatory protein (SSP) acting as auto-antigen, to which T-Lymphocytes from patients with rheumatoid arthritis respond, identified in synovial fluid has been found to bind to a hirudin-agarose affinity chromatography matrix.[32]