Do a search and you'll find that spironolactone. topical doesn't have any systemic absorption problems.
Is it effective? Well, as in any other "remedy", it helps some men and doesn't help other men. It's not a cureall.
I use Bryan's recipe. Six, 100mg tablets, crushed and mixed in 20ml of a neutral beauty cream like Cetaphil or Neutrogena. Bryan uses Dermovan, it is a neutral cream used by dermotologists.
Oh, I forgot to mention that Bryan suggests keeping it in the refridgerator. That's what I do.