The use in medicine of stars (the 12 signs of the zodiac) and of the sun, moon and planets is an ancient practice. However, the practice reached its epitome in Europe in the late medieval (1450+ AD) and early modern periods (1700 AD).
During this period, medical practitioners regarded different signs of the zodiac and planets as having governance over different parts of the body, as controlling different diseases, and as affecting the usefulness of different drugs.

Medieval medicine heavily relied on the connection between the health of the body and the state of the world. Medical status was associated with the the stars or the the body's humors, and a patients' health was determined by the position or balance of these extra-corporeal elements. 

The signs of the zodiac and planets were believed to have governance over different parts of the body, different diseases, and the effectiveness of different drugs. From the brain to the feet, from Ares to Pisces, from Mercury to Venus, the health and status of a human body seemed constantly dependent upon extraterrestrial bodies.

In addition, four internal fluids of the body needed to remain in balance in order to keep a person in balance. Too much of one fluid or too little of another led to illness, ill-temperament, and more. A person's natural state was also attributed to the four humors: blood, phlegm, black bile, and yellow bile.

1. Astrology and Medicine
2. Medicine and the Planets
3. Humoral Medicine