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There have been multiple reports of excessive shedding several months after finasteride therapy. Typically, there is a good response to finasteride to prevent or reverse MPB. Then, around the 11th to 16th week, there can be sudden shedding, sometimes on a massive scale. The entire phenomenon fits the description of a telogen effluvium. It is a common observation that post-partum women often suffer the same temporary hair loss. In the case of finasteride use, the telogen effluvium appears to be a reaction to the sudden change in the systemic levels of the sex hormone, DHT. Often the cause of a telogen effluvium are obscure, but has been related to high fevers, stress, trauma, medications, etc.

The shedding is generally diffuse (global) and can affect areas of the scalp not usually affected by MPB. So, it would be common to note shedding from the sides and back of the head in addition to the crown, vertex and frontal areas. The shedding tends to be fairly symmetrical, but will be more noticeable in the areas affected by MPB, because there is a higher ratio of hairs in the telogen phase than in the other areas of the scalp.

The duration of a telogen effluvium is variable, but rarely lasts more than a few months and there is invariably complete restitution unless another pathologic process also occurs.

As a rule, treatment is not necessary because the hair will grow back. For most patients, there is no evidence of residual loss of hair within a year. However, there have been cases of patients taking finasteride and reporting repeated bouts of excessive shedding. In this situation, it would be advisable to discontinue use of finasteride in favor of alternative anti-androgens.