What Is Simethicone Made Of: Ingredients Explained

Simethicone is a mixture of polydimethylsiloxane (a type of silicone oil) and silicon dioxide (silica). That two-ingredient combination is the active substance in virtually every over-the-counter gas relief product, from chewable tablets to infant drops. The silicone oil does the antifoaming work, while the silica keeps it dispersed evenly so it can coat gas bubbles throughout your digestive tract. What surrounds that active ingredient, though, varies widely depending on the product form, and the full ingredient list tells a more interesting story than the label suggests.

The Active Ingredient Up Close

Polydimethylsiloxane, often abbreviated PDMS, is a long-chain polymer built from repeating units of silicon and oxygen atoms, with methyl groups hanging off each silicon. If you have ever handled pure silicone lubricant or touched a silicone baking mat, you have a rough sense of the material’s feel. It is oily, slippery, chemically inert, and does not dissolve in water. Those properties make it an exceptionally good antifoaming agent: when a thin film of PDMS contacts a gas bubble trapped in liquid, it destabilizes the bubble’s surface tension and causes it to collapse.

On its own, though, PDMS would just sit as an oily layer in your stomach. The silicon dioxide mixed in acts as a dispersing agent, breaking the silicone oil into tiny particles that spread through gastric fluid rather than clumping together. This combination is what gets labeled “simethicone” on your medicine bottle. The ratio of PDMS to silica varies by manufacturer, but the basic pairing is universal across brands.

Inactive Ingredients in Typical Formulations

The simethicone itself is only part of what you swallow. Every product includes inactive ingredients that shape the texture, taste, shelf stability, and delivery method. A liquid infant gas relief product, for example, lists carboxymethylcellulose sodium, citric acid, natural flavors, microcrystalline cellulose, polysorbate 60, potassium sorbate, purified water, sodium benzoate, sorbitan monostearate, sorbitol, and xanthan gum among its inactive ingredients.¹ Each of those serves a specific purpose:

• Carboxymethylcellulose sodium and xanthan gum: thickeners that keep the liquid at a consistent viscosity so the simethicone stays evenly suspended rather than separating.
• Microcrystalline cellulose: another stabilizer that prevents clumping and helps the emulsion pour smoothly.
• Polysorbate 60 and sorbitan monostearate: emulsifiers that keep the oily simethicone and the water-based carrier from splitting apart in the bottle.
• Citric acid: adjusts acidity to keep the formula stable and palatable.
• Sorbitol and natural flavors: sweetener and taste-masking, particularly important in infant and children’s formulations.
• Potassium sorbate and sodium benzoate: preservatives that prevent microbial growth in the liquid.
• Purified water: the base of the liquid emulsion.

Chewable tablets and softgel capsules have different inactive ingredient lists. Tablets typically include binders like calcium phosphate or cellulose, disintegrants that help the tablet break apart in your stomach, and flavoring agents. Softgels encase the simethicone in a gelatin shell, sometimes with added glycerin to keep the capsule flexible. The active ingredient is the same across all these forms; what changes is the engineering around it.

How Simethicone Actually Works in Your Gut

Gas in your digestive tract exists mostly as small bubbles trapped in mucus and food residue. These bubbles create that uncomfortable bloated, pressured feeling. Simethicone does not reduce the total amount of gas your body produces, and it does not prevent gas from forming. What it does is physically change the bubbles.

When the silicone-silica mixture contacts a gas bubble, it lowers the surface tension of the film surrounding that bubble. The bubble wall becomes too weak to hold its shape and collapses. Small trapped bubbles merge into larger ones, which are easier for your body to expel through belching or flatulence. Think of it as popping soap bubbles in a bathtub: the water and air are still there, but the foam disappears. This is a purely mechanical action, not a chemical reaction with your body’s tissues or digestive enzymes.

What Happens to It in Your Body

Simethicone is not absorbed through the lining of your gastrointestinal tract. It passes through your system intact and leaves in your stool. Because it never enters your bloodstream, it has essentially no systemic effects, which is why it carries an unusually wide safety margin and is approved for use in newborns.² There is no known lethal dose in humans, and overdose reports in poison control databases are vanishingly rare.

This non-absorption is also why simethicone has so few drug interactions. It stays in the gut lumen and does not compete with other drugs for liver metabolism or kidney excretion. However, “so few” is not “zero,” and there is one interaction worth knowing about.

The Levothyroxine Interaction

If you take levothyroxine for an underactive thyroid, simethicone can interfere with how much of that medication your body absorbs. The mechanism is thought to involve intraluminal binding, where the simethicone physically binds to the levothyroxine in your gut before the thyroid drug can cross into your bloodstream. A systematic review found that this malabsorption can be resolved by either stopping the simethicone or separating the dosing times so the two are not in your stomach simultaneously.³

The practical takeaway: if you are on thyroid medication, take it on an empty stomach as usually recommended and wait at least 30 to 60 minutes before taking simethicone. For most other common medications, simethicone does not pose absorption problems, precisely because it does not interact chemically with much of anything.

Simethicone for Infant Colic

One of the most common uses of simethicone is in infant gas drops marketed to parents of colicky babies. The logic seems sound: if the baby is crying because of gas, collapse the gas bubbles and the crying should stop. The evidence, however, tells a different story.

A randomized, placebo-controlled multicenter trial in infants found that the likelihood of improvement was the same whether the infant received simethicone or placebo. About 28 percent of infants responded only to simethicone, 37 percent responded only to placebo, and 20 percent responded to both. The researchers concluded that simethicone was no more effective than placebo for treating infantile colic.⁴ A Cochrane review of pain-relieving agents for colic reached a similar conclusion, finding no difference in daily hours of crying or in the proportion of infants who responded positively to treatment when comparing simethicone to placebo.⁵

A systematic review of reviews and guidelines looking at common interventions for infantile colic rated simethicone’s evidence as moderate to low, showing no benefit or a negative effect.⁶ The fact that the placebo response rate in these trials was so high suggests that many parents perceive improvement simply because colic tends to fluctuate on its own. Simethicone is safe for infants, which is why it remains on shelves, but the evidence base for its effectiveness against colic is genuinely weak. Parents who feel it helps their baby are likely seeing a combination of natural fluctuation and the psychological comfort of doing something.

Medical Uses Beyond the Medicine Cabinet

The same antifoaming properties that make simethicone useful for bloating have given it a second career in medical procedures. During upper gastrointestinal endoscopy, foam and air bubbles inside the stomach and esophagus can obscure the camera’s view, making it harder for the physician to spot abnormalities. A common solution is to have the patient drink a simethicone preparation before the scope goes in.

A controlled trial found that patients who received simethicone before esophagogastroduodenoscopy had significantly less gastric foam compared to those who received placebo. The endoscopy procedure was also about a minute shorter in the simethicone group, which, while modest, adds up over a busy endoscopy suite’s daily schedule.⁷ The same study noted that duodenal foam was not significantly reduced, suggesting the simethicone works best in the stomach where it has the most contact time. Simethicone is also sometimes added to bowel-prep solutions before colonoscopy, where persistent bubbles can similarly block the view of the colon lining.

Simethicone in the Food Industry

If you have ever read the ingredient list on a fast-food cooking oil, a bottled sauce, or a fountain drink syrup, you may have noticed “dimethylpolysiloxane” or the European additive code E900. That is essentially the same silicone polymer that forms the backbone of simethicone, used as an antifoaming agent during food processing. In deep fryers, for instance, it prevents oil from foaming up dangerously when moisture from food hits hot fat. In beverage production, it keeps carbonated liquids from foaming over during filling.

Analyzing and quantifying these silicone-based antifoaming agents in food is difficult because of their polymeric nature, which has led to ongoing work developing better testing methods.⁸ The amounts permitted in food are tightly regulated and extremely small, typically measured in parts per million. At those concentrations, the silicone does its antifoaming job during manufacturing and is present only in trace amounts in the finished product.

The presence of the same base polymer in both a gas relief pill and a fast-food fryer sometimes alarms people who encounter the fact online. The context matters, though. Water is also an ingredient in both industrial coolant and baby formula. Polydimethylsiloxane at food-additive concentrations is biologically inert, just as simethicone is at therapeutic doses. It passes through you without being absorbed, regardless of whether it arrived in a gelcap or a chicken nugget.

What Happens to Simethicone in the Environment

Because simethicone is excreted unchanged and also enters the environment through industrial and personal care products, researchers have studied where it ends up. Dimethicone (the PDMS portion) tends to accumulate in sediments and soils rather than dissolving in water, which makes sense given that it is an oil that does not mix with water. Related cyclic siloxanes, which are used in personal care products, partition into the atmosphere instead.

In both cases, degradation starts with a non-biological step and then proceeds biologically. The end products are carbon dioxide, silicic acid (a naturally occurring form of silicon found in sand and quartz), and water.⁹ This means the silicone does not persist indefinitely in the environment. It breaks down, just slowly. Silicic acid is one of the most abundant natural compounds in the Earth’s crust, so the final degradation product is essentially returning silicon to where it came from.

Why the Ingredient List Varies So Much Between Products

Walk down the antacid aisle and you will see simethicone sold as a standalone product, combined with calcium carbonate for heartburn plus gas relief, bundled with loperamide for diarrhea and gas, or mixed with aluminum and magnesium hydroxide in liquid antacids. In each case, the simethicone component is the same PDMS-plus-silica mixture, but the surrounding ingredients change dramatically based on what else the product is trying to do.

Combination products add their own active ingredients and their own inactive ingredients, which means the total ingredient list can balloon. A liquid antacid containing simethicone might include aluminum hydroxide, magnesium hydroxide, sorbitol, flavoring, and various preservatives. A chewable gas-and-acid tablet might add calcium carbonate, sucrose, dextrose, and coloring agents. If you are trying to avoid a specific ingredient for allergy or dietary reasons, checking the inactive ingredient list on the specific product matters more than just knowing the product contains simethicone.

Dosage also varies between forms. Standard adult simethicone doses range from 40 to 125 milligrams per dose, taken up to four times daily, with a typical maximum around 500 milligrams per day. Infant drops are dosed at 20 milligrams per dose. Because simethicone is not absorbed, these doses are determined more by what effectively coats the gut contents than by any concern about blood levels or organ toxicity. The upper limit exists mainly because there is no benefit to taking more, not because higher doses are dangerous.

Veterinary and Exotic Animal Use

Simethicone turns up in veterinary medicine as well, particularly for species prone to gastrointestinal gas accumulation. Rabbits, guinea pigs, and chinchillas can develop painful and sometimes life-threatening gas bloat, and simethicone is one of the first-line treatments exotic animal veterinarians reach for. The logic is the same as in humans: collapse the gas bubbles so the animal can pass the gas. In rabbits especially, gastrointestinal stasis accompanied by gas buildup is a common emergency, and simethicone’s safety profile makes it a practical option even when a precise diagnosis is still being worked out.

Birds and reptiles have also been treated with simethicone in clinical settings, though the evidence base for these species consists mainly of case reports and clinical experience rather than controlled trials. The dose is scaled down dramatically for small animals, and the liquid infant formulation is often the product used because it is easy to dose with a syringe. The same inactive ingredients that make the drops palatable for human babies turn out to work reasonably well for a reluctant rabbit, too.