Daily adult vitamins. An over-the-counter adult multivitamin (+/- minerals) is fine for a teenager to take once a day. If a teen doesn't eat or drink much in the way of dairy products, then an adult vitamin d and calcium tablet is also needed. Some people just take a Tums smoothies once a day for their calcium supplement. Vitamin d and multivitamins are even available in "gummy" chewables for adults now.