It has been known for some time that deficiency in B7 (biotin) can lead to hair loss and other, far worse conditions. So the argument is taking extra will increase hair growth etc. I'm not aware that there is a toxic level of B7, there are toxic levels for other vitamins. So you shouldn't have bad side effects.
But you can always take raw egg yolks, very high in biotin. But they have to be raw and avoid the egg white which contains avidin which has a very high avidity for biotin. Mmm maybe a pill is more pleasant.
Cindy