The clinical practice of administering chemicals to patients for the treatment of disease is known as chemotherapy and the academic study of such chemicals as pharmacology. A major problem is the specificity of the drugs employed. It is now clear from extensive clinical experience that any chemical introduced into a patient will have a multiplicity of actions. Some may be desirable and some undesirable. It is the balance between these two effects which determines whether or not a particular drug is considered clinically useful. If morphine is given to a patient in order to relieve severe pain, then its other effect of causing constipation may be regarded as a side-effect. However, the same action may be usefully employed when treating a patient with diarrhea, when its action in causing constipation is advantageous. Under ideal circumstances we would like to administer drugs which exert only one single effect on the body and that this would be adequate to treat the particular symptom or disease from which the patient was suffering. However, no such drugs exist for cancer.
