I'm trying to gain weight but my metabolism is very how how can i get it to slow down.

Weight gain: It all depends on why you want to gain weight. One easy test that can show a fast metabolism is a TSH. A very low TSH may mean your thyroid is hyperactive. The cause of this requires further blood tests.

Eat and exercise.: You need to focus your exercise regimen more on weight training than aerobics. As well, make sure you eats lots of food, and focus on complex carbohydrates and lean protein sources. We don't focus on slowing down a fast metabolism; we work with it.