ranger, do a search on here for people running T3 without gear.
There are plenty of people that run 25mcg/day or even 50mcg/day while not on anything and don't report excessive muscle loss. Personally I wouldn't go over 25mcg/day though.
Of course taking it with clen and/or a steroid (especially oxandrolone) would be better...
Also T3 is anabolic/catabolic depending on dosage. Small dosages actually improve insulin's action and protein metabolism, which is why many people take 12.5mcg/day while on bulking cycles and/or with insulin.