Having hypothyroidism is it safe to take prenatal vitamin and biotin even if i'm not pregnant?

Yes: Having hypothryroidism does not affect your need for vitamins. The only concern is that taking calcium supplements can interfere with absorption of thyroid hormone, so if the penatal vitamin has calcium take it at least 2 hours after taking thyroid. Also, i advise having your doctor check your free T3 level- if not in the upper half of the normal range consider adding liothyronine (t3).