Cabergoline

The verdict

Our read at a glance.

Whether an approved treatment for a pituitary disorder is appropriate for managing a side effect a person is choosing to create.

The signal

The approved use is well supported: cabergoline lowers prolactin and is a first-line treatment for hyperprolactinaemic disorders including prolactinomas, with labelled products and a continuing trial literature in endocrinology and in lactation suppression. The off-label use in this population is not supported by trials. It rests on the assumption that the sexual dysfunction associated with 19-nor steroids is prolactin-mediated, which is only partly true: those compounds also act directly at the progesterone receptor, and lowering prolactin does not address that pathway.

The unknown

Whether the valvular risk documented at the higher, sustained doses used in Parkinson's disease extends to the lower intermittent doses used in this context. The data were never generated in this population, so the answer is unknown rather than reassuring.

Our read

The pattern this memo is really about is stacking a second prescription drug to manage the consequences of an unapproved first one. Cabergoline is a good drug for the disease it treats. Taken to offset a self-inflicted hormonal problem, it adds a valve risk and an impulse-control risk to fix something that is partly not even prolactin-driven.