Hypromellose, Stearates and Silicon Dioxide: Reading the Small Print Under the Supplement Facts

The Supplement Facts panel is built around dietary ingredients: the vitamins, minerals, herbs and other materials the product is sold for. On Harmo Brain that means magnesium and the six names in the 575 mg blend. But a capsule cannot be made from those alone. Powders have to be held in a shell, kept from sticking to the machinery, and encouraged to flow evenly into that shell on a filling line. The materials that do those jobs are not dietary ingredients, so they do not belong on the panel. The federal rule gives them their own place. Ingredients in dietary supplements that are not dietary ingredients, it says, such as excipients, fillers, artificial colours, artificial sweeteners, flavours or binders, are included in the ingredient list (21 CFR 101.4). The same section says that where some ingredients, meaning sources, are identified within the nutrition label, the list outside it is headed "Other ingredients". The Harmo Brain magnesium row names its source, magnesium glycinate, and the bottle prints exactly that heading.

The same section says ingredients required to be declared on a food label go in descending order of predominance by weight. So the five names under this panel are a ranking, just as the six names inside the blend are. On this bottle the line reads: Hypromellose (Vegetable Capsule), Microcrystalline Cellulose, Magnesium Stearate, Stearic Acid, Silicon Dioxide. That order fits what you would expect: the shell first, as the heaviest piece, then the bulking agent, then the two lubricants, and last the flow aid. Nothing on the label gives an amount for any of them, so the ranking is all there is.

Hypromellose, also called HPMC, is a cellulose derivative, and in capsules it stands in for gelatin. A 2010 review of the literature on HPMC capsule shells describes it as the plant-based replacement for the animal-derived gelatin used in conventional two-piece capsules, and it surveyed the evidence on whether it is a suitable substitute (Al-Tabakha 2010). That is why the label writes "Vegetable Capsule" in brackets after the word: it tells you the shell is not gelatin.

Does the shell material change what your body receives? One randomised crossover study compared ibuprofen in HPMC capsules with matching gelatin capsules in two groups of eight healthy volunteers, one group dosed by mouth and one rectally. It found no marked differences in bioavailability, and concluded that the two shell materials can be regarded as interchangeable from a biopharmaceutical point of view. In a separate laboratory test on isolated porcine oesophagus, the HPMC capsules were also less inclined to stick (Honkanen 2002).

There is a counter-example worth knowing about, because it shows that the shell and the fill can interact. In a laboratory study, a green tea extract was filled into gelatin and into HPMC capsules. All of them disintegrated within 30 minutes, but the gelatin capsules showed an immediate-release dissolution profile in every test medium and the HPMC ones did not, especially in a fed-state medium. The authors attributed the delay to an interaction between the tea's catechins and the shell, and recommended checking dissolution before releasing a supplement (Glube 2013). That was one botanical and one set of test conditions. It says nothing about Harmo Brain. Its value here is as a reminder that "the capsule is just packaging" is usually true and occasionally not, and that the way to know is a dissolution test, which the label does not report and this website does not have.

Put the three shell studies side by side and the sensible conclusion is a cautious one. The review frames HPMC as a credible replacement for gelatin. The crossover study found the two interchangeable for one drug. The green tea study found that a particular botanical behaved differently in the two shells. Each is true within its own conditions, and none is a general rule.

The practical reading is the same as for any capsule: the shell is probably neutral for most fills, and a dissolution test is how a maker would confirm that for a particular one. A buyer cannot run that test. What a buyer can do is notice whether the label and the seller talk about it at all. On this label and this website, they do not, which is the honest state of affairs for most supplements and a fair thing to record.

Microcrystalline cellulose is a form of cellulose used as a filler, the material that adds bulk when the active powders alone would not fill the capsule evenly. Silicon dioxide, a fine silica powder, does a different job: it coats powder particles so that they slide past one another instead of clumping. A laboratory study of colloidal silicon dioxide as a glidant used exactly this pairing, mixing it with microcrystalline cellulose, and found that it improved the flow of the cellulose powder, with the effect depending on the type of silica and how the powder was mixed (Jonat 2004).

Neither of these two is doing anything for your brain, and neither pretends to. They are the reason the powder in the capsule is consistent from the first capsule in a batch to the last. When a label's panel lists a small blend and a large total, this is where the remaining bulk goes.

The two stearates are the ones people ask about most, often because the word "magnesium" appears in one of them. It is worth doing the arithmetic, since the panel's 80 mg of magnesium is the one number on the label that is quoted often. Magnesium stearate has the formula C36H70MgO4 and a molar mass of 591.2 g/mol (PubChem). Magnesium's atomic weight is 24.305, so magnesium makes up 24.305 divided by 591.2, or about 4.1%, of the compound by weight. Ten milligrams of magnesium stearate would therefore contain about 0.4 mg of magnesium, and even a hundred milligrams would contain about 4 mg. The label does not say how much of it there is. But whatever the amount, it cannot approach the 80 mg the panel declares, and the panel states that the 80 mg is magnesium supplied as magnesium glycinate from the blend.

What magnesium stearate is known for, in formulation science, is a side effect: it can slow dissolution. A 2016 study of metformin tablets found that magnesium stearate delayed the dissolution of tablets in acid, and traced the mechanism to the material accumulating on the tablet surface, with stearic acid formed from it in acidic medium (Ariyasu 2016). That study was of tablets, with a different drug, and the abstract itself calls the delay a known property of the lubricant. It is a reason dissolution testing exists, not evidence of a problem in this capsule.

Stearic acid, a saturated fatty acid with the formula C18H36O2 (PubChem), is also found in ordinary food. A review of human studies of its effect on blood lipids concluded that, compared with other saturated fatty acids, it lowers LDL cholesterol and that its overall effect is more favourable than that of trans fats (Mensink 2005). Those results concern stearic acid as a dietary fat, which is a different scale from a lubricant in a capsule, and the label gives no amount. The point is only that the material is not exotic.

One thing the label leaves open is the source of the stearates. Stearic acid and its salts can come from vegetable or animal fats, and the panel does not say which. The seller's artwork carries a vegetarian mark, and the shell is a vegetable capsule. If the source matters to you for religious, ethical or dietary reasons, the honest step is to ask before you buy, using the details on the contact page, and to treat an answer you cannot get as an answer.

They are uncommon, and worth a proper look if you have known sensitivities. A review of excipient hypersensitivity in drugs and vaccines calls these reactions rare, notes that suspicion should be high when anaphylaxis has occurred with several chemically distinct products, and lists gelatin, carboxymethylcellulose, polyethylene glycols and propylene glycol among the common culprits (Caballero 2021). None of those is on the Harmo Brain other-ingredients line, and the shell is a plant-derived HPMC rather than gelatin. That is a reading of the list against the review, not a promise that nobody will react to anything on the bottle. A person with a history of reactions to supplements or capsules should still read the whole line and speak to an allergist or pharmacist.

Those five questions take about a minute and apply to any capsule on any shelf. For the other half of this label, the six names in the blend and what the order and the total let you work out, the blend arithmetic article is the companion piece, and the Supplement Facts page shows the whole panel, including the "Other ingredients" line, in one place.

Put together, the five other ingredients describe an ordinary, plainly made capsule: a plant-derived shell, a filler, two lubricants and a flow aid. Nothing on the printed list is an active ingredient. The one real unknown is the same as with any supplement: the label does not say how quickly the capsule releases its contents, and that is information only a dissolution test would give.

That is not a reason to worry, and it is not a reason to skip the line. Reading it once tells you what you are swallowing, what the shell is made of, and what to ask if something matters to you. And if you have a question the label cannot answer, the contact page is the place to start.