Magnesium Stearate CAS 557-04-0

What is Magnesium Stearate?

Magnesium stearate is the magnesium salt of stearic acid, C₃₆H₇₀MgO₄ — although in practice it is never a single compound, because commercial stearic acid is always a mixture of stearic and palmitic acids. The monographs recognise this and specify the ratio rather than pretending otherwise.

It is a very fine, light, white powder that feels greasy and adheres to the skin. That greasiness is the functional property: under compression it shears into a thin film between the tablet and the die wall, so the tablet ejects cleanly instead of sticking or scoring.

It is used at 0.25 to 2% of tablet weight, which makes it one of the smallest components of most formulations and one of the most consequential. Too little and tablets stick; too much, or blended too long, and the same film that prevents sticking also prevents bonding and blocks water from reaching the tablet core.

Commercially it is the near-universal solid dose lubricant, with no equivalent substitute at its price and performance. It is supplied in vegetable-source grades for pharmaceutical use, with bovine-derived material now rare in regulated supply chains, and it is also used in cosmetics, food and as a polymer processing additive.

Why magnesium stearate specifically

• Effective at very low levels. A quarter of a percent to two percent is enough, so it lubricates without displacing active or filler and without dominating the formulation.
• Shears into a film under pressure. The plate-like crystal structure slips along its layers, which is exactly the property a boundary lubricant needs.
• Works on the die wall and the punch. It lubricates ejection and prevents sticking to the punch faces, which are two different problems usually solved together.
• No real substitute at the price. Alternatives exist — sodium stearyl fumarate, stearic acid, glyceryl behenate — but each trades cost or performance, which is why magnesium stearate remains the default worldwide.

How Magnesium Stearate is Manufactured

Magnesium stearate is made by combining a magnesium salt with stearic acid or its sodium salt. The route and the fatty acid feedstock together decide the physical form, which is what actually determines performance.

• Fatty acid selection. Commercial stearic acid, derived from vegetable oils for pharmaceutical grades. The stearic to palmitic ratio comes from this choice and is a monograph parameter.
• Precipitation route. Sodium stearate solution is reacted with magnesium sulphate or chloride, precipitating magnesium stearate, which is filtered, washed and dried. The dominant pharmaceutical route — it gives a fine, high-surface-area product.
• Fusion route. Stearic acid is reacted directly with magnesium oxide or hydroxide. Simpler, but gives a denser, lower-surface-area material with different lubrication behaviour.
• Drying and hydrate control. Drying conditions determine whether the product is anhydrous, monohydrate or dihydrate. This is invisible on a basic certificate and strongly affects lubrication performance.
• Milling and classification. Final particle size and specific surface area are set here — the two figures that best predict how the material will behave in your blender.

Typical Commercial Specification

Figures below are representative of pharmacopoeial vegetable-source material. Specific surface area, particle size and hydrate form can be specified where your process depends on them — tell us what you need.

Physical & Chemical Properties

Behaviour in the formulation

Magnesium stearate is a boundary lubricant, and almost every formulation problem it causes comes from the same property that makes it work:

• Film formation under shear. Blending shears the plate-like particles into a thin hydrophobic film across the surfaces of the other powder particles. That film lubricates the die wall and the punches.
• Hardness reduction. The same film sits between particles that would otherwise bond, so tablet hardness falls as blending continues. This is the over-blending effect, and it is time-dependent rather than concentration-dependent alone.
• Dissolution retardation. Being hydrophobic, the film slows water penetration into the tablet, which can push dissolution out of specification without any change to the formula.
• Chemical interaction. It is slightly alkaline and reacts with acid-sensitive actives — aspirin and some vitamins notably — and with many alkaloid salts.
• Hydrate dependence. The dihydrate lubricates differently from the anhydrous form, so a change in hydrate state between lots changes performance even when every compendial test passes.

Magnesium Stearate vs the Alternative Lubricants

Every alternative to magnesium stearate exists to solve one of its two problems: the hydrophobic film or the alkaline reactivity. Each solves it at a cost.

Stated plainly: nothing else lubricates as well at 0.5%. The alternatives are chosen when the active will not tolerate an alkaline excipient, when dissolution is marginal, or when a robust process matters more than excipient cost — and all three are good reasons, but they remain exceptions rather than the rule.

Industries We Supply Magnesium Stearate To

The same light white powder goes to a tablet press, a capsule filler and a cosmetic pressing line. What changes between them is the source declaration, the surface area and the documentation each sector expects.

Where Magnesium Stearate is Used

Magnesium stearate does one job in most formulations, but it does it in several ways. These are the uses our customers buy it for.

As a tablet lubricant

The job is boundary lubrication at the die wall: without it, ejection force rises, tablets score and the press eventually stalls. The complication is that the same film that reduces friction also reduces inter-particle bonding, so there is an optimum rather than a maximum. Most formulations land between 0.5 and 1%, and the blending time matters as much as the level — which is why a formula that works in a small lab blender often fails in a high-shear production blender running the same recipe.

The over-blending problem

This is the single most common excipient-related failure in tablet manufacture. Extending the lubricant blend time shears the particles further and spreads the hydrophobic film more completely, so tablet hardness falls and dissolution slows — with the formulation, the equipment and the excipient lot all unchanged. The control is to add the lubricant last, blend for a short defined time, and treat that time as a critical process parameter rather than a procedural detail.

Where it cannot be used

Magnesium stearate is slightly alkaline and reacts with acid-sensitive actives. Aspirin is the classic case, and several vitamins and many alkaloid salts behave similarly. Where the interaction is real, stearic acid or sodium stearyl fumarate are the usual substitutes — the first because it is not alkaline, the second because it is both less reactive and less hydrophobic, at a considerably higher price.

Quality Control & Testing

Every lot is released against a batch-specific Certificate of Analysis written against the monograph you nominate, with the functional parameters that actually drive lubrication reported alongside the compendial tests.

• Magnesium content — the compendial assay, confirming identity and salt stoichiometry.
• Fatty acid composition — stearic acid content and the stearic plus palmitic total, both monograph parameters that reflect the feedstock.
• Specific surface area — the figure that best predicts lubrication performance, reported where specified.
• Loss on drying — related to hydrate state, which affects how the material lubricates.
• Bulk density and particle size — practical predictors of blending behaviour and dispersion in the blend.
• Chlorides, sulphates and heavy metals — compendial purity and elemental impurity control.
• Microbial limits — total aerobic count, yeasts and moulds, and absence of specified organisms per the monograph.

Common Process Problems & Likely Causes

When magnesium stearate causes trouble on a press, the cause is usually blending rather than the lot. This table is the shortcut our technical desk works through before anyone opens a complaint file.

Packaging, Storage & Shipping

• Standard packing. 20 or 25 kg net in multi-ply bags with polyethylene inner liners, or in fibre drums, palletised and shrink-wrapped.
• Low bulk density. This is a very light powder, so a 25 kg bag is physically large. Allow for the volume in warehouse planning and in charging equipment sizing.
• Storage. Cool, dry and well-ventilated, off the floor, away from strong acids, alkalis and oxidising agents.
• Dust control. It aerates very easily and the dust travels. Charge under local exhaust ventilation and keep it away from open product.
• Screening before use. Screen before addition to the blend. The powder agglomerates lightly in the bag, and unscreened lumps give uneven lubrication.
• Cross-contamination. Being hydrophobic and very fine, it transfers readily to surfaces and equipment. Dedicated scoops and careful cleaning between products.
• Shelf life. Typically 36 months in unopened original packing under those conditions. Re-test loss on drying and microbial limits rather than assume.
• Transport classification. Not classified as a dangerous good for transport.

Hazards & Safe Handling

Magnesium stearate is a benign material with no significant toxicity by any normal route, used in oral and topical products and permitted in food. The handling considerations are physical rather than toxicological.

• Dust explosion risk. Like any fine organic powder, airborne magnesium stearate presents a dust explosion hazard, and its very low bulk density means it aerates readily. Earth and bond transfer equipment and control ignition sources.
• Slip hazard. Spilled powder is slippery underfoot — it is a lubricant, after all. Clean spills promptly and completely.
• Nuisance dust. Not toxic, but airborne dust irritates the respiratory tract mechanically. Local exhaust ventilation at charging and dispensing points.
• Eye contact. Mechanical irritation only. Safety glasses during dispensing and transfer.
• PPE. Dust mask where dust is generated, safety glasses and normal plant workwear. No special chemical protection is required.
• Housekeeping. The fine hydrophobic powder spreads and settles on surfaces well beyond the point of use. Regular cleaning prevents both the slip hazard and cross-contamination.
• Spill response. Sweep or vacuum avoiding dust clouds; it does not wash away readily, being water-repellent.
• Environment. Not hazardous to the aquatic environment. Dispose as ordinary industrial waste in line with local regulations.

Regulatory & Compliance Notes

Magnesium stearate is a compendial excipient and an approved food additive, with monographs in all the major pharmacopoeias. Because obligations differ by territory and use, the notes below are orientation rather than legal advice — confirm your own position with your regulatory adviser.

• Pharmacopoeial status. Monographs in IP, BP, Ph. Eur. and USP-NF. We supply against the monograph you nominate, with a compliance statement on the COA.
• Source declaration. Pharmaceutical grades are vegetable-derived, with BSE/TSE statements supplied as standard. Source is a common customer and regulatory question, so it is declared explicitly rather than left to inference.
• Food additive status. Permitted as E470b in food applications in the major regulatory systems, within the conditions that apply in your market.
• Elemental impurities. Heavy metal and elemental impurity control per the applicable monograph and guideline. Tell us if your filing requires specific element testing.
• Excipient GMP expectations. Supply chains for compendial excipients increasingly expect documented GMP and supplier qualification. Tell us what your quality agreement requires.
• Halal and kosher. Certification available on request, and frequently specified for this product because of the fatty acid origin question.

We Supply Magnesium Stearate Worldwide

Chelora Chemicals is a supplier and export partner, not a single-plant trader. We ship Magnesium Stearate from India to customers across Asia, Europe, the Middle East, Africa, and North and South America, handling the export documentation, pharmacopoeial documentation and freight so the material arrives ready to use.

• Incoterms. EXW, FOB, CIF, CFR and DAP quoted to suit your purchasing terms and freight arrangements.
• Ports. Regular shipments through Nhava Sheva (JNPT) and Mundra, with other Indian ports arranged where it suits the routing.
• Documentation. Commercial invoice, packing list, certificate of origin, COA, SDS and the vegetable source, BSE/TSE and halal statements issued as a complete set.
• Flexible volumes. A single bag for laboratory qualification, through LCL consolidations, up to repeat full container loads on a supply contract.
• Supply continuity. Because we are independent of any one producer, a plant turnaround or a shipping disruption at one source does not have to become your stock-out.

Buying Magnesium Stearate from Chelora

We are an independent sourcing and supply partner. For magnesium stearate that means settling two things at enquiry: whether you need a defined specific surface area, because the monograph does not control it and your tablet hardness depends on it, and whether your active is acid-sensitive — because if it is, this may not be the right lubricant at all.

• Documentation on every lot. Batch-specific COA written against the nominated monograph, with surface area and bulk density where specified, plus SDS, TDS and source statements.
• Samples before commitment. Trial quantities for blend and compression qualification ahead of a commercial order.
• Quantities. From a single 25 kg bag through to full container loads on contract supply.
• Vegetable source as standard. Pharmaceutical grades are vegetable-derived, with BSE/TSE, halal and kosher documentation available.
• Export experience. Packing, labelling and export documentation handled for sea and air freight.
• Related excipients. MCC, lactose monohydrate, povidone and HPMC from one supplier, which keeps a whole solid dose formula on a single order.

How ordering works

• Send the enquiry. Product, grade or pharmacopoeia standard, quantity, destination port and the Incoterm you buy on. If you have a spec sheet, attach it — it saves a round trip.
• We quote. Price, lead time, packing and a sample COA, normally within one working day.
• Sample and qualify. For first orders or critical applications, we send a trial quantity so your lab can sign off before you commit.
• Confirm the order. Proforma invoice issued; payment terms agreed against the volume and the relationship.
• Production and QC. Material allocated and released against a batch-specific COA, with a pre-shipment sample where the application calls for it.
• Ship and document. Packed, labelled and loaded with the full export document set, and tracked through to arrival.

Related Pharmaceutical Excipients & Intermediates

Buyers of magnesium stearate usually source several of these alongside it — it appears in almost every solid dose formula alongside a filler, a binder and a disintegrant. Consolidating them on one order cuts freight cost and gives you a single point of contact for documentation.