I personally have no experience of it, there are many brand names and similar products out there - this is worth a read...http://medical-dictionary.thefreedictio ... ogen+Drugs
A lot of research needs to be done with transgender people. And trans* people are still in effect Guinea Pigs when it comes to medicating. Usually once you find an agreeable medication then people tend to stick with it. In all honesty, I think when medics prescribe they are taking a bit of a shot in the dark in as much as you are. However, there is no substitute for a blood test and monitoring, as they can act more quickly and check if it is actually working or not. The problem with antiandrogens for prostate cancer and their dosage, maybe that they do not want to fully impair the male libido in patients, so may not be as potent as goserelin (Zoladex). And without medical supervision then you would not be certain if it was doing anything at all.
If you have been on HRT for some time unless you are self-medding (which doctors are more than aware of) then speak to a gender specialist or gender hormone specialist (Endocrinologist) even if you have to pay privately for a one-off to pick their brains.
The trouble with anecdotal, "My friends says..." or "I know someone who takes this..." is that they may have a completely different reaction to you. In the same way some are allergic to Penicillin. They have to simply take an alternative. But it has to be discovered first. And unless you want to experiment on yourself - which you are free to do of course - then just be careful.