I just bought biotin 300 mcg including 100 tablets. but i heard it reccomended taking 3000 mcg a day which means 10 a day for me.. is that dangerous?

Very safe: Biotin is not known to be toxic. Doses of to 5000 mcg/day were well-tolerated for 2 years in a research study and up to 15, 000 mcg/day in shorter studies. While that sounds like a lot, 3000 mcg= 3 mg and many vitamins are safe in much higher amounts. See http://lpi.Oregonstate.Edu/infocenter/vitamins/biotin/ for more info.

I don't know: Why it's been prescribed. Usual recommended doses are:7 to 10 years of age: 30 mcg. Adolescents and adults— 30 to 100 mcg. If it was only recommended and not prescribed at that dose, then i would not take more than 1 a day. It is a b vitamin (vitamin h) and the extra will be peed out. You can't get 1, 000 mcg a day anyway since only 3 of the tabs is 900mcg. Ten tablets would be 3, 000 mcg or 3 mg.