Can a 14 year old take 300 mcg biotin supplements? my sister wants to use it as she is seeing bald spots on her scalp.

Shouldn't be needed: There are no vitamins, herbs, supplements, or foods that are proven to slow or stop hair loss in a normal healthy person. Maintaining a balanced diet of healthy foods, and taking one multivitamin + minerals tablet each day, should keep a person in normal, good nutritional status. Perceived hair loss in a teen or young person should be checked by her doctor, to see if there is real, true hair loss.