I was looking at molecular structure of Test, Deca and Tren, and it seems that Stew is right, everything indicates that Tren should be 5-alpha reduced.
Lets take a look how does it happen with Testosteron.
The double bond between carbons 4 and 5 gets reduced(removed) and two hydrogen atoms are added, one at carb 4 and one at carb 5.
The -alpha- in 5-alpha reductase means that the hydrogen that is added in carbon 5 is added -alpha- to the ring, and ends up under or behind the ring, when viewed in 3-D.
Now, lets look at structure of Nandrolone. It has the same double bond between same 4 and 5 carbons( very important for it to be the same, otherwise "the key" of 5-alpha reductase will not fit)
We all know that Nandrolone gets 5-alpha reduced, so comparing its structure with Test, we can have general idea of what kind of structure will underdo that conversion.
Now, lets compare structure of Nandrolone and Trenbolone:
Nandrolone
Trenbolone
As you can see Trenbolone is almost identical to Nandrolone with exception of one extra double bond in second ring and one in third, but those have no effect on 5-alpha binding.
The conclusion is that unless for some reason Trenbolone has very low affinity to 5-alpha reductase(like EQ and Dianabol do, for example) it should be 5-alpha reduced.
One more thing, even it gets 5-alpha reduced, doesn't mean that it's safe for hair, comparing to Deca, because being 3 times stronger androgen then Test, it will be reduced to still pretty much strong androgen, wich we can compare to Test, but a way stronger then DHN.