How long before meds help my new kitty with hyperthyroidism??

It's been almost a week since I rescued my kitty, Paul.  He has been diagnosed with hyperthyroidism and prescribed Methimazole.  Poor baby is skin and bones.  The first few days he had barely eaten but these last couple days he acts like he cant get enough food.  He is a very large cat (frame wise).  We joke and wonder if we brought a mountain lion into our home.  He only weighs 7 lbs.  I am trying to get some weight on this boy.  He seems to have pepped up a little bit since we started the meds. He is at least ten years old so I don't expect him to be as active as my other kitties.  But he is such a sweet boy who clearly had a rough time out on the streets..  I just wish I knew when I would start seeing major improvements. 

As a general rule it takes 2 weeks at a minimum before the methimazole starts to show results. 

One of the symptoms of hyperthyroidism in cats is that no matter how much they eat,  they still feel hungry.  (the over-active thyroid makes their thermostat and general metabolism run too high)  Is he having loose bowel movements?  Another sign of hyperthyroidism. 

So,  be patient,  be vigilant about giving him his meds at the same time each day,  give him absolutely as much canned food as he asks for,  even if it seems like too much. 

When he starts putting on weight and not being so hyper about food that will be the sign that he has turned the corner.

No doubt the vet told you to return in 30 days and get his T-4 levels checked,  right? 

I am bringing him back to the vet in 4 weeks to be checked.  I have been feeding him small amounts of food because if I just let him eat what he wants, he ends up throwing up.  He did good yesterday. No vomiting.  No loose bowel movements.  And he seemed to have a little bit more energy.  I give him his meds around the same time every morning and night.  I am a very routine person so that wont be a problem. I just have zero experience with this so I don't know if he acting how he is supposed to. Poor baby needs some meat on his bones.