In his voluminous writings, Avicenna [981-1037 CE] laid out the following rules for testing the effectiveness of a new drug or medication. These principles still form the basis of modern clinical drug trials.

1. The drug must be free from any extraneous accidental quality.

2. It must be used on a simple, not a composite, disease.

3. The drug must be tested with two contrary types of diseases, because sometimes a drug cures one disease by its essential qualities and another by its accidental ones.

4. The quality of the drug must correspond to the strength of the disease. For example, there are some drugs whose heat is less than the coldness of certain diseases, so that they would have no effect on them.

5. The time of action must be observed, so that essence and action are not confused.

6. The effect of the drug must be seen to occur constantly or in many cases, for if this did not happen, it was an accidental effect.

7. The experimentation must be done with the human body, for testing a drug on a lion or a horse might not prove anything about its effect on man.