Cultural, ethnic, and environmental influences on medical therapy add to the complexities encountered by practicing health care professionals. Ignoring such studies may inadvertently result in increased patient suffering, an increase in side effects, or both. Pharmacokinetic drug differences, especially polymorphism, are more relevant if the patient's condition is severely compromised and the drug has a narrow therapeutic range. However, if the drugs is carefully selected and the dosage is calculated according to the patient's therapeutic response, adverse outcomes can usually be reduced.