I don't think Trenbolone is 5a reduced... But it's late and I'm not willing to double check..
I feel it's more likely due to the highly androgenic nature of trenbolone, itself.. it scores 500:500 on the anabolic/androgenic scale.. opposed to testosterones 100:100..
I ran a tren/sust cycle probably 2 yrs ago and am prone to mpb. Actually i'm about 1/2 gone of my once super thick scalp and maintaining with propecia. When i ran this cycle i stayed on the finasteride and saw now signs of any additional loss. I'm starting to think that sides are totally different for each of us and there really is no accurate way to know until you try it.