My vet has always recommended Proscar (5 mg) or Propecia (1 mg) - both contain finesteride, and they shrink the prostate. I have used it successfully and with no noticable side effects on 4 ferrets. Also, I believe Dr. Bruce Williams, DVM of the AFIP has discussed using it for ferrets ... I remember that it was rather expensive, hope someone can offer a more reasonable source. hope this helps .... [Posted in FML 5944]