Hair thinning or loss is a side effect of hyperthyroidism, if your levels are too high this is definitely a possibility. is it permanent? probably not, unless you're running it high dose and continually losing hair for long periods of time.
Hypothyroidism can also cause hair loss. Had a buddy who had very low t3.. his hair over the years became very thin and wispy.. wirey.. once diagnosed and put on meds his hair returned to it's normal old self. Thyroid is a bitch lol
Low dose, I would be lying if I told you I remembered exactly and I didn't log it. It was fast and it happened both with T4 and T3, I didn't learn my lesson the first time. Everyone is different but for me personally anything thyroid fucks me up all around and I know it happens to others too. Nothing fucked me more than thyroid meds, not tren not any AAS.