Most dietary supplements contain more than just the active ingredient on the front label. Fillers, flow agents, preservatives, sweeteners, and colorants make up the “Other Ingredients” list at the bottom of the panel, and some of them deserve a closer look before you buy. Not every additive is harmful, but a handful have enough evidence against them to warrant skipping when better options exist.
Artificial Preservatives: BHA and BHT
Butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are synthetic antioxidants added to supplements, particularly oil-based capsules and softgels, to prevent fats from going rancid. They’re cheap and effective at extending shelf life, which is why manufacturers favor them. The concern is hormonal. In vitro studies show BHA has a weak estrogen-mimicking effect and anti-androgenic properties, placing it in the category of potential endocrine disruptors. Compounds in that category have been linked to reduced sperm quality, increased incidence of hormone-sensitive cancers, thyroid disruption, and reproductive system abnormalities. The evidence isn’t conclusive enough for an outright ban, but it’s strong enough that many supplement brands have moved to alternatives like mixed tocopherols (a form of vitamin E) or rosemary extract for the same preservative function.
Hydrogenated Oils and Trans Fats
Partially hydrogenated oils were once common in softgel capsules and as fillers in powdered supplements. The FDA revoked all authorizations for partially hydrogenated oils in food in August 2023, recognizing that trans fats raise LDL (“bad”) cholesterol while lowering HDL (“good”) cholesterol, increasing the risk of heart disease, stroke, and type 2 diabetes. Despite this, some imported or older-stock supplements may still contain them. Check the ingredient list for “hydrogenated” or “partially hydrogenated” oil of any type. Fully hydrogenated oils don’t contain trans fats, but they’re still highly processed saturated fats that serve no nutritional purpose in a supplement.
Artificial Sweeteners in Powders and Gummies
Protein powders, greens blends, and gummy supplements frequently contain artificial sweeteners like sucralose or acesulfame potassium (ace-K) to improve taste without adding calories. Research in mice found that just four weeks of ace-K consumption significantly altered gut bacterial composition, reduced the gut’s ability to digest and ferment carbohydrates, and lowered levels of beneficial fermentation byproducts like lactic acid and succinic acid. Researchers concluded that these disruptions could increase the risk of chronic systemic inflammation. Sucralose has shown similar effects: a study in rats found it impaired the growth of gut bacteria.
These are animal studies, so the direct translation to humans isn’t settled. But if you’re taking a daily supplement specifically to support your health, choosing one sweetened with stevia or monk fruit avoids the question entirely.
Maltodextrin as a Cheap Filler
Maltodextrin is a starch-derived powder used as a bulking agent and filler in capsules, tablets, and powdered supplements. It has a glycemic index comparable to pure glucose, meaning it spikes blood sugar rapidly. Your body digests and absorbs maltodextrin at essentially the same rate as glucose, producing a nearly identical insulin response. For most people taking a single capsule, the amount is too small to matter. But if you’re using a powdered supplement daily where maltodextrin is listed as one of the first ingredients, the cumulative carbohydrate load can be meaningful, particularly if you have diabetes or insulin resistance.
FD&C Red No. 3 and Synthetic Dyes
In January 2025, the FDA issued an order revoking the use of FD&C Red No. 3 in food and ingested drugs, citing the Delaney Clause, which prohibits food additives shown to cause cancer in humans or animals. This dye has been used in gummy vitamins, chewable tablets, and liquid supplements for decades. While other synthetic dyes like Yellow No. 5, Yellow No. 6, and Blue No. 1 remain permitted, they’ve been associated with behavioral sensitivity in some children. If color serves no functional purpose in a supplement, there’s no reason to accept it.
Titanium Dioxide: A Controversial Coating
Titanium dioxide gives tablets and capsules a clean white appearance. In 2021, the European Food Safety Authority concluded it could no longer be considered safe as a food additive, largely because a concern for genotoxicity (DNA damage) couldn’t be ruled out. The EU subsequently banned it. However, Health Canada reviewed the same body of evidence and reached the opposite conclusion, finding no health concerns at current exposure levels and determining that a precautionary approach wasn’t warranted. The disagreement hinges on study methods: many of the concerning results came from experiments using ultrasonically dispersed nanoparticles, which Health Canada argued don’t represent how titanium dioxide actually behaves in food.
Oral toxicity is known to be low in multiple animal studies, and absorption through the digestive tract appears to be negligible. Still, it’s purely cosmetic. If you’d rather not be part of the ongoing debate, plenty of supplements use alternatives or skip the coating entirely.
Magnesium Stearate: Overhyped Concern
Magnesium stearate is the ingredient that generates the most online alarm with the least scientific backing. It’s a flow agent that prevents supplement powders from clumping and sticking to manufacturing equipment. When you swallow it, it breaks down into magnesium and stearic acid, the same fatty acid found abundantly in cocoa butter, olive oil, and beef. Stearic and palmitic acids are normal dietary fats that your body metabolizes through standard energy pathways. The compound holds GRAS (Generally Recognized as Safe) status in the United States, is approved in the EU, China, Japan, Australia, and New Zealand, and showed no genotoxic potential in bacterial, chromosomal, or bone marrow tests. Claims that it blocks nutrient absorption have no credible evidence behind them.
Heavy Metal Contamination
Heavy metals aren’t listed as ingredients, but they’re one of the most important things to watch for in supplements. Lead, arsenic, mercury, and cadmium can contaminate products through soil, water, or poor manufacturing controls. Under USP pharmaceutical standards, the permitted daily exposure from a product is 5 micrograms for lead, 15 micrograms for inorganic arsenic, and 30 micrograms for inorganic mercury. These are maximums, not targets. Herbal supplements, protein powders, and products sourced from countries with less soil regulation tend to carry the highest contamination risk. Independent testing organizations like NSF International and ConsumerLab regularly find products exceeding these limits.
Even manufacturers following the FDA’s current Good Manufacturing Practice guidelines aren’t guaranteed to be free of all contaminants. GMP requires internal quality testing and limited screening for adulterants, but it doesn’t mandate the kind of comprehensive third-party analysis that catches trace metal contamination reliably.
Proprietary Blends That Hide Dosages
A proprietary blend is legal shorthand for “we’re not telling you how much of each ingredient is in here.” Under the Dietary Supplement Health and Education Act, manufacturers must list the total weight of the blend and name every ingredient inside it, but they don’t have to disclose individual amounts. This means a blend listing “500 mg proprietary blend: ashwagandha, rhodiola, lion’s mane” could contain 490 mg of the cheapest ingredient and 5 mg each of the others. You have no way to verify whether you’re getting a meaningful dose of any single component.
This isn’t an “ingredient to avoid” in the traditional sense, but it’s the single most reliable red flag on a supplement label. If a company is confident in its formulation, it lists exact amounts. Proprietary blends exist to protect profit margins, not trade secrets.
How to Read Labels More Effectively
The “Supplement Facts” panel lists active ingredients with dosages. The “Other Ingredients” section below it is where fillers, flow agents, preservatives, sweeteners, and coatings appear. This is where most of the ingredients discussed above show up. Scan this section first when evaluating a new product.
Third-party testing certifications offer the most practical shortcut. NSF Certified for Sport screens not only for label accuracy but also for undeclared compounds, contaminants, and banned substances. USP Verified means the product contains what the label claims, dissolves properly, and was manufactured under safe conditions. Products without any third-party seal aren’t necessarily dangerous, but they’re asking you to trust the manufacturer’s internal testing alone.
A shorter “Other Ingredients” list is generally better. The active ingredient is what you’re paying for. Everything else is there to make the product cheaper, prettier, tastier, or easier to manufacture. Some of those additives are harmless. Others, like BHA, artificial sweeteners, and synthetic dyes, have enough questions around them that alternatives exist for a reason.