Spiro isn't the only anti androgen out there, even in the us where Androcur isn't sold there are things like Bicalutamide. If you and your doctor have a talk I am sure you can find something that works for you (or if not medication there is always an orchie for T reduction).
I imagine metabolism is a factor but probably not the only factor, people's bodies just seem to react differently, when I was first on spiro I was dizzy and tired and nearly passing out often, the after about 8 months on Bicalutamide I went to spiro again (it is so cheap) and had none of the issues I had the first time, so I feel there is a huge amount of variability in the reaction to this medication.