April 24, 2026
Do prenatal vitamins make you gain weight?
Do prenatal vitamins make you gain weight?
No, prenatal vitamins do not cause weight gain. They contain vitamins and minerals and there’s no mechanism by which a prenatal supplement directly adds body fat or increases the number on the scale.
This is one of the most common misconceptions about prenatals, and it's easy to see where the confusion comes from: many people start taking prenatals around the same time they become pregnant, and pregnancy involves weight gain. The two are correlated in timing but not in cause.
RELATED: How to choose a prenatal vitamin
What the science says
There is no clinical evidence linking prenatal vitamin use to weight gain in non-pregnant or pregnant individuals. A 2022 meta-analysis of individual participant data from 14 trials and over 45,000 women found that multiple micronutrient supplements (MMS) were associated with greater gestational weight gain compared to iron and folic acid alone, but this finding was specific to pregnant women in low- and middle-income countries where baseline nutritional status was often poor. The weight gain in this context was considered a positive outcome (reducing the risk of inadequate gestational weight gain and small-for-gestational-age births), not a side effect.
Why you might feel heavier
Some people experience bloating or constipation from the iron in prenatal vitamins, and these GI effects can temporarily affect how your body feels and how your clothes fit. This isn't actual weight gain. Staying hydrated, eating fiber-rich foods, and talking with your provider about iron form options can help manage these symptoms.
If you're pregnant, weight gain is a normal and expected part of the process. The amount varies based on your starting weight, but the Institute of Medicine recommends a total gain of 25-35 pounds for people starting at a normal BMI. This weight includes the baby, placenta, amniotic fluid, expanded blood volume, breast tissue, and fat stores your body needs for breastfeeding.
What about when you're not pregnant?
If you're taking prenatals and not pregnant, the vitamins themselves will not cause weight gain. If you notice a change on the scale, look at other lifestyle factors: diet, activity level, stress, sleep, and hormonal fluctuations all play a much larger role.
RELATED: Can men take prenatal vitamins? What to know about male prenatal nutrition
A note from WeNatal on do prenatal vitamins make you gain weight
WeNatal for Her uses iron bisglycinate, which is less likely to cause the bloating and constipation that can make people feel like they've gained weight. If past prenatal experiences left you feeling puffy and uncomfortable, the form of iron matters more than most people realize. Don't let this myth keep you from taking a supplement that supports your health and your baby's development.
RELATED: The ultimate preconception guide: What to do when you’re ready to get pregnant
References
Adams JB, et al. (2022). Evidence based recommendations for an optimal prenatal supplement. Maternal Health, Neonatology and Perinatology, 8:4. DOI: 10.1186/s40748-022-00139-9
Liu E, et al. (2022). Effects of prenatal nutritional supplements on gestational weight gain in low- and middle-income countries: a meta-analysis of individual participant data. American Journal of Clinical Nutrition, 116(6):1864-1876. DOI: 10.1093/ajcn/nqac259
