Weight Gain Vitamins
If you want a vitamin that will make you hungry, you should take Vitamin B-12, which will cause you to eat more and thereby raise your weight. Multivitamins are known to cause the reverse effect, causing people to lose weight (except pregnant women with HIV) instead of gaining. If you want to use a vitamin to gain weight, then try B-12, if that doesn't work, then you should either go to the doctor to diagnose if you have a problem keeping you from gaining weight, or try to gain weight by drinking protein shakes. Change your eating habits to eating five or six meals a day and eating a little bit smaller meals. This will cause you to eat more calories, which will increase your weight in a more natural and gradual way.
Weight Gain Foods
Vitamins and minerals are not known to cause weight gain, but if you eat foods that are high in protein and carbs but not in fat, then you will be able to gain weight. Foods like bread and pasta are great because they are carb loaders. Especially when combined with a low fat meat, like lean beaf hamburger. This will raise the amount of calories while minimizing the amount of fat that you intake. Spaghetti, lasagna, and other foods like that make for great weight gaining foods.
If you have a strong desire to gain weight, please remember that gaining more than 1 or 2 pounds a week is really bad for your body. Do not get carried away and try to gain 3 or 4 pounds in a week. And remember, even though you are only gaining a pound a week, that is 4 pounds a month, and 52 pounds a year. You will only have to do it a couple of months to get up to the weight that you want to have.