Professor Rui-Ping Xiao, founder of Hope Medicine, "this study is the first ever to show that prolactin receptor blockade can promote hair growth in patients with androgenic alopecia and may provide a novel therapeutic approach."HMI-115 doesn't block the production of prolactin. My understanding is that it binds to prolactin receptors (PRLR) and alters its shape to where prolactin can still bind to it but the resulting signal transmission is disrupted.
The effects are presumably drastically different than inhibiting prolactin, especially considering serum prolactin levels may end up increasing on HMI-115.
Interestingly growth hormone also binds to PRLR.