Taking prenatal vitamins when not pregnant is generally safe, but it's important to be aware of potential side effects. Prenatal vitamins may contain higher doses of biotin, which can promote hair growth, but the results may vary depending on the individual. While prenatal vitamins are unlikely to cause weight gain, some may contain added calories or sugar, so choosing a supplement that fits your overall diet is important. Some prenatal vitamins may also cause constipation due to the high iron content, so drinking plenty of water and eating a fiber-rich diet is important. You should always consult your healthcare provider before starting any new supplement. The benefits of prenatal vitamins are substantial.