Heredity may make some people more susceptible to the toxic effects of certain drugs. The realm of mind-body interactions, including such aspects as mental attitude, outlook, and belief in self and confidence in health care practitioners, remains largely unexplored. In general, the number and severity of adverse drug reactions increase as the dose increases. However, this dose-response relationship doesn't apply to people who are allergic or hypersensitive to a drug. For these people, even small amounts of the drug can trigger an allergic reaction, ranging from minor and simply annoying to severe and life-threatening.
Doctors usually ask if a person has any known drug allergies before prescribing a new drug.
People who have had severe allergic reactions, who have serious medical problems, or who are taking high-risk drugs should wear a Medic Alert necklace or bracelet. A lower risk of overdose toxicity is often the reason doctors prefer one drug to another when both drugs are equally effective. For example, if a sedative, antianxiety drug, or sleep aid is needed, doctors usually prescribe benzodiazepines such as diazepam and triazolam rather than barbiturates such as pentobarbital. Benzodiazepines are not more effective than barbiturates, but they have a wider margin of safety and are much less likely to cause severe toxicity in case of an accidental or intentional overdosage. Safety is also the reason why newer antidepressants such as fluoxetine and paroxetine have largely replaced older but equally effective antidepressants such as imipramine and amitriptyline.