12.5mcg will 'supercharge' the thyroid, doses of 25-50 are considered equal to that which the body produces. When taking exogenous T3 you will cause supression of the thyroid gland and the thyroid will reduce its T3 output to maintain honeostasis.
Even 12.5mcg may be too much, I'm testing that doseage now and all seems well.
I started with a high T3 dose when I first cycled the drug and I think my crash was when I went below 50mcg on the taper off the stuff so my body may produce more than 25mcg.
If you need to take a high dose make sure it is worth it, as I have already said 25mcg - 50mcg is a replacement dose that possibly wont yield any positive results so the next step would be 75mcg-100mcg otherwise it just isnt worth the risk IMHO.