I learnt my very first lesson with cytomel the hard way when without running any anabolic substance, i ran 150mcgs of T3 every day and lost 35kgs of fat but every pound of muscle too and was reduced to skin and bones.
It was then that i learnt that T3 also eats muscle.
I then started cycling and after a couple of cycles leant to start using t3 sensibly with next to no muscle loss.
Hypo thyroidsm has never been a problem even after i ran cytomel for over 8 weeks straight. The trick i found is to taper down though. I would ramp it to a maximum of 125mcgs and keep tapering down once every 4 days thereabouts.
Only, when i'm totally off the cytomel, i would be very srtict on my overall caloric intake for about a month or so and slowly start increasing calories.