The Surprising Things To Know When Taking A Multivitamin For The First Time

As popular as multivitamins are, it’s always a good idea to ask questions and be well informed about anything you put in your body. We’re each unique—and there are a lot of different products out there—after all.

First and foremost, know this: “Multis are safe at their core,” says Ferira. “There are always exceptions to the rule for irresponsible brands, but I’m talking about reputable, high-quality, clean brands here.”

That said, there are a few things to be aware of when taking a multivitamin. One big one? In some cases, your multivitamin could interact with certain medications you take, according to dietitian Jessica Cording, R.D., CDN, author of The Little Book of Game-Changers. If you take medication to reduce blood clotting, for example, talk to your doctor before taking any supplement that contains vitamin K (or when significantly changing your dietary vitamin K intake, for that matter) since the vitamin contributes to blood clotting and can thus be counterproductive to blood thinning.* 

Research also suggests that smokers and former smokers may want to avoid large amounts of beta-carotene (the precursor to vitamin A found in plant foods and many supplements). Excess vitamin A may also have negative impacts on pregnant women, but as with most things in nutrition, there’s some nuance to consider.

Ferira explains, “when we’re talking about vitamin A toxicity, there are specific retinoic acid metabolites that are actually found in certain drugs, not supplements, that are genuinely bad for baby’s development.” Even though that type of vitamin A and science doesn’t apply to supplements, “out of an abundance of caution, pregnant women should avoid supplements with 10,000 I.U. (3,000 mcg) or more of preformed vitamin A, which is the retinol form. This ‘upper limit’ doesn’t apply to the beta-carotene vitamin A form at all.”

One caution relevant to multivitamins that’s super clear cut is iron poisoning in young children. Ferira explains, “This concern of accidental pediatric iron overdose is exactly why multivitamins that contain iron include warnings on their labels, explicitly calling out this risk and directing the consumer to keep out of children’s reach.” So to repeat: Keep out of reach of children (who may mistake your multi capsule, tablet, etc., for candy).

One less serious consideration to keep in mind? Some people may experience digestive upset after taking multivitamins, depending on the formula and when they take their supplement. “For some individuals, including myself, taking a multivitamin first thing in the morning—whether on an empty stomach or not—simply doesn’t jibe with our biology,” Ferira says. “A high-quality multivitamin should feature an array of macro- and microminerals in its formula—but it is not uncommon for that mineral load to be too much for one’s stomach in the a.m.” Luckily, simply taking your multi with lunch should put that issue to bed.