The word “Hijama” in the Arabic language comes from “Hajama” or “Ahjama”, which respectively mean “to return to its original volume”, and “to not go forward”. 

Hijama is a prophetic medicine, which consists of removing or drawing “bad blood” by small incisions on the skin. The argument for this method is that as a young man ages, and his physical growth stops at the age of 22, bad blood starts accumulating in his veins which disturbs blood circulation, and thus makes the person susceptible to all kinds of diseases. Therefore, “Hijama” returns blood to its natural volume, after the bad blood has been drawn.
Similar medicinal methods have been performed in older civilizations, and as recently as the 20th century. The Chinese used cupping as a type of massage therapy, blood letting was performed sometimes using a pricking needle, before applying the cup over the area in order to create suction. This technique was used to promote blood circulation, remove stasis, and alleviate swelling and pain.
In Islam, The prophet Mohammed (PBUH) said that: “Al-hijama, is the most beneficial medicine for people”, Narrated by Al-Bukhari.
Many literatures refer to Hijama as cupping, where as cupping can be performed with a cup or a horn with no blood letting involved, Hijama practitioners may use a cup for suction, and the method always involves blood letting. Hijama incisions are done on different parts of the body, depending on the illness, puncturing the veins ,”Fased”, is required in some cases.
There are differences about best days or times of day/month to perform Hijama, some advise to always perform it in the middle of the lunar month, since blood raises to the surface. However, in the presence of a disease, it can be performed anytime it’s needed.
In some traditional Muslim societies, Hijama, as I witnessed, was done simply with a razor, and the practitioner, who usually inherits the knowledge from his ancestors, decides where the incisions occur according to the patient’s ailment.
To increase its effectiveness, Hijama is most beneficial when it’s performed after a good night sleep, with no food in the stomach, in the middle of the lunar month, and in the spring season when it’s warm but not too hot or too cold. It’s not recommended for women who are menstruating, or children who are still growing.
Donating blood, which can be considered another method of blood letting, has been proven to help reduce the risk of heart attack, by reducing the amount of iron in the blood. The iron is said to increase the rate of the oxidation of cholesterol, which increases damage to arteries, and thus can result in cardiovascular disease. Menstruating women are at less of a risk than adult men, since they lose some of that excess iron during their period.
These latest findings by modern medicine interject with the old practice of cupping or Hijama, in the fact that there are benefits to drawing blood from a human body to maximize its strengths and defenses against disease.

References:

1- The Prophetic Medicine, Ibn Qayem Al-Jozeyah.

2- http://www.itmonline.org/arts/cupping.htm

3- http://en.wikipedia.org/wiki/Hijama

4- http://archives.cnn.com/2000/HEALTH/04/26/give.blood.wmd/