Taking vitamins does not make a person gain weight. However, there are numerous prescription medications, including antidepressants, birth control pills, beta-blockers and cancer medications, that can cause increased appetite and weight gain, states Fox News.
Being deficient in certain vitamins can also make a person more prone to gaining weight, reports Fox News. If a person isn't getting enough vitamin D, iron or magnesium, his metabolism rate tends to slow. This can result in weight gain from lack of energy and a decreased activity level. Adding vitamins should be done under a doctor's supervision to prevent drug interactions or accidental overdoses.