Drug-Induced Alopecia

Abstract

Hair loss is a common complaint, and an understanding of the hair cycle is vital in order to interpret whether hair loss is secondary to medication use, as the use of prescription medications is widespread. When there is a temporal association between the onset of hair loss and the commencement of a medication, the medication is commonly presumed to have caused the hair loss. Drug-induced alopecia is a result of either rapid termination of the normal growth phase (anagen effluvium) or a premature conversion of actively growing hairs into the dormant, resting phase (telogen effluvium). Hair loss, in particular telogen effluvium, may, however, occur in response to a number of triggers including fever, hemorrhage, severe illness, and stress. Because hair loss is often delayed and because diffuse alopecia often begins sub-clinically, it may be challenging to determine the primary of alopecia. As a rule of thumb, adverse drug reactions are reversible provided the causative drug is avoided; however, identifying the culprit medication can be difficult. This chapter will review the normal hair cycle and discuss the major drugs that have been associated with alopecia, along with their mechanism (s) of action.