Yup, it can do that.

I think the stickied FAQ at the top of the forum might help you answer a lot of your questions. The typical treatment is they'll give you T4 which your body can convert to T3 as needed, some people take both in the form of porcine thyroid and they like that. To me, the T3 was too strong and made me feel hyper. It is quite hard to find a doctor that'll prescribe the "natural" thyroid hormone.

Taking thyroid medication will NOT cause weight gain, in fact, if you're hypothyroid it'll probably cause weight loss. Thyroid hormone has been around for a looong time. I wouldn't even call it a drug, it's a hormone.

Good luck!