My hair is weak and thin, 17 yrs, is biotin useful, will a 1000 mcg dose affect my weight?

Probably shouldn't: Biotin deficiency is rare, but can occur in persons with genetic mutations, on long-term antibiotics or anti-convulsants, or who eat a lot of raw egg whites. There is no good evidence that this over-the-counter supplement is the magic potion to grow hair or prevent hair loss. Biotin is safe to take but 1000 mcg per day is over 6 times the usual dose, so shouldn't be taken by a normal healthy teen.