Drugs are substances that change chemical reactions in the body
MEDICAL DRUGS relieve pain and illness from the body
RECREATIONAL DRUGS are used for enjoyment like alchahol or tobacco

1.) The drugs are tested using computer models and human cells grown in the laboratory. Many substances fail this test because they damage cells or do not seem to work.

3.) Drugs that have passed animal tests are used in clinical trials. They are tested on healthy volunteers to check they are safe. Very low doses of the drug are given to begin with. If there are no problems, further clinical trials are done to find the optimum dose for the drug.