Get access to everything we publish when you sign up for Outside+.
Reading supplement labels can be tricky because what you see doesn’t necessarily tell the full picture. Here’s the problem: the supplement industry isn’t tightly regulated, and oversight can be limited, even lax. Plus, vitamins, herbs, and other formulations aren’t as rigorously tested as pharmaceuticals, sourcing information for raw materials isn’t required, and the end product may not be verified for quality, purity, and potency.
The result? Your supplement could be laced with heavy metals, environmental toxins, GMOs, allergens, hidden animal ingredients, and other nasty additives that have no place in your diet.
To help you become a savvy supplement shopper, let’s get acquainted with what those ingredient names really mean.
Your supplement may include a variety of corn- or soy-derived ingredients (citric acid, glycerin, soy lecithin, maltodextrin, cellulose, isoflavones, lactic acid, sorbitol), either used in the manufacturing process or added as active compounds. Since at least 90 percent of corn and soybeans grown in the United States are genetically engineered: unless the label explicitly states otherwise, your capsules, tablets or powders are likely to contain GMOs.
Some vitamins, especially vitamins E and C, may also be sourced from soy and corn, and vitamin B12 supplements are made from genetically modified microbes. And many amino acids are produced through a fermentation process that uses genetically engineered bacteria.
Supplement Smart: To be sure your supplement is free of genetically modified organisms, look for the Non-GMO Project Verified logo; or choose products with a certified organic seal.
Some are obvious, like whey, fish oil, bee pollen, and gelatin — mainly in capsules and softgels. Other animal-derived ingredients are less conspicuous. Lanolin, used to produce vitamin D3 supplements, comes from sheep wool. L-cysteine, an amino acid, is commonly manufactured from hair or feathers. Magnesium stearate or stearic acid, used as a processing agent, often comes from animal fats, usually pork. Carmine, a red food coloring, is made with crushed cochineal insects. Glucosamine and chondroitin are generally sourced from seafood (also allergenic). And digestive enzymes are likely to contain animal products, including ox bile, lipase, pork-derived pepsin, trypsin, and pancreatin.
Supplement Smart: When you’re buying supplements — especially digestive enzymes and vitamin D — choose those clearly marked as vegan, or look for the “Certified Vegan” logo guaranteeing it’s free from animal products or byproducts.
Binders, fillers and flow agents are “inert” ingredients frequently used in the manufacturing process to compress tablets, create bulk, prevent clumping, and optimize movement through production machinery. These are not active ingredients, but they’re not as “inert” as you might think — and they aren’t required by law to be listed on the label.
Additives like cellulose, lecithin, and maltodextrin often contain GMOs. Flow agents (stearic acid or magnesium stearate) may be derived from animal sources; talc, unless it’s listed on the label as “USP talc,” can have traces of asbestos, a known carcinogen. Other additives, like potassium sorbate and carrageenan, are linked with sensitivities, nausea, gastrointestinal distress and inflammation. Plus, some research suggests magnesium stearate interferes with the body’s ability to absorb nutrients.
Supplement Smart: Buy supplements that clearly state “free from binders, fillers or other additives” on the label; or look for the Non-GMO Project Verified and Certified Vegan logos to avoid genetically modified organisms and animal products.
A wide array of synthetic food dyes are approved by the FDA, but there’s plenty of evidence that many of them are potentially harmful. In studies, a number of dyes have been shown to cause sensitivities and reactions; some were contaminated with benzidine and other carcinogens.
Research also suggests that synthetic food colors impact the immune system, activate inflammation, promote intestinal permeability, and lead to cross-reactions and neurobehavioral disorders. Other studies link artificial colors with increased hyperactivity, irritability, and behavioral changes in children. Carmine is associated with significant sensitivities and severe allergic reactions. And titanium dioxide, used as a whitening agent, can trigger intestinal inflammation and is considered a potential carcinogen.
Supplement Smart: Stick to supplements with no added colors, or choose those that use (ideally organic) natural colors derived from fruits and vegetables, like beets, carrots, blueberries, or chlorophyll.
Flavors and sweeteners
You’re right to be wary of artificial flavors. Mostly used in chewable tablets, gummies, liquids, syrups, and powder mixes, they’re manufactured by extracting chemicals from petroleum, wood pulp (a common source for vanilla flavor) and other inedible ingredients.
But natural flavors aren’t without their issues. The term simply means it’s derived from any kind of edible product. That includes meat, dairy, eggs or seafood — not vegan-friendly, and potentially allergenic.
As for sweeteners: fructose, dextrose, glucose and sorbitol are usually sourced from corn, so they’re likely to contain GMOs. Fructose and other highly processed sweeteners also fuel inflammation—especially in the lining of blood vessels, a known risk factor for heart disease. Plus, many protein powders are laced with staggering quantities of sugar — as much as 23 grams per serving; even modest amounts of sugar in gummies and chewables add up fast. Sugar-free supplements aren’t much better — some “natural” alternatives like sugar alcohols are notorious for causing digestive distress.
Supplement Smart: Buy unsweetened, unflavored options, or look for supplements sweetened with stevia and/or monk fruit.
Besides GMOs, hidden animal ingredients, and allergenic additives your supplements might also be tainted with some really nasty toxins. In studies, a variety of fish oils and other dietary supplements were found to be contaminated with heavy metals, including cadmium, lead, and arsenic.
Along with heavy metals, fish oil may contain mycotoxins, pesticide residues, and significant levels of PCBs and dioxins (a family of chemicals that have similar toxicity) — linked with reproductive and developmental problems, immune system, and hormone disruptions, and cancer.
Fish oils aren’t the only culprit. A number of herbal formulas, especially Chinese and Indian preparations, were shown to have toxic amounts of heavy metals, some exceeding the safe daily consumption limit. Even low levels add up; if you’re taking a slew of supplements every day, you’re at risk for cumulative, potentially dangerous levels of exposure.
Supplement Smart: Choose molecularly distilled fish oil, and look for brands that conduct third-party testing—ideally certified by USP or NSF International; most companies will also provide Certificates of Analysis. For herbal formulas, stick to reputable brands and certified organic herbs.
Pharmacologically active ingredients
Tainted supplements, misleading labels, and illegal active ingredients are more common than you might expect. A disturbing number of undeclared pharmaceuticals or their synthetic analogs have been identified, most frequently in weight loss and sexual enhancement formulations.
In research, many were laced with undeclared stimulants, appetite suppressants, and sexual performance pharmaceuticals, some were discontinued or banned for safety concerns. Sports supplements have been shown to contain untested or banned compounds — not listed on the label or misidentified as botanical extracts — linked with liver damage, cardiac arrest, and even death.
Other studies point to widespread discrepancies between ingredient panels and actual content, with lower levels of active ingredients and, in some cases, unidentifiable chemicals.
Supplement Smart: Be selective — choose reputable, well-known brands with transparent websites and third-party testing. And be wary of internet companies, unrecognizable brands, or “proprietary blends” that don’t identify specific ingredients.
If you want to learn more about supplements, read more here: