Drugs exert their healing power in the human body by a (more or less well-known) pharmacological effect. Their effectiveness can be observed in the mitigation of disease symptoms (e.g. a cough with a cold) or it can be measured by physiological values (e.g. blood pressure lowering with high blood pressure). One speaks of a side effect or adverse drug reaction (ADR) when therapeutically undesired effects occur (e.g. allergies). If they are not tolerable, the therapy must cease in the worst case. Herbal medicines generally do not have many side effects, but attention must be given to the possible side effects.