Research it. It's a shampoo and the active ingredient is Ketoconazole, which has shown to be very effective at stopping/slowing/reversing hair loss topically.
You can buy 1% from Wal-Mart or 2% by prescription.
When you shower, lather your head up with it and let it sit there for about 5 minutes or so. Do it daily while on cycle. The bottle is small, but it goes a long way unless you have really long hair.
If you can get a hold of spironolactone tabs, grind them up and mix them in with the Nizoral. Ketoconazole + spironolactone is considered by many one of the best topical solutions for treating hairloss.
But, if you can't get spiro, just use the Nizoral.
When you're off cycle, you should probably continue using it a few times per week. AAS use only speeds up pre-existing hairloss (androgenic alopecia), so using it regularly could help you keep more of your hair longer.