Mannitol as a Pharmaceutical Excipient: Properties and Applications

Mannitol is a six-carbon polyol, or sugar alcohol, and a stereoisomer of sorbitol. It occurs naturally in small amounts in most vegetables and was historically extracted from manna, the dried sap of the manna ash.

Commercial mannitol is now made by catalytic or electrolytic hydrogenation of sugars such as glucose, fructose or mannose. US food regulations (21 CFR 180.25) also permit fermentation routes using specified microorganisms.

The same molecule is used in two very different ways. As one of the inactive pharmaceutical excipients in a formulation, it is a filler, sweetener or bulking agent. As an active pharmaceutical ingredient, it is given intravenously as an osmotic diuretic or inhaled in some respiratory products. The two uses call for different grades, specifications and regulatory files, so buyers should state clearly which one they need.

Mannitol's defining properties are very low hygroscopicity, no Maillard reactivity, a sweet taste with a cooling feel, good water solubility and three crystal polymorphs. Together they explain where formulators use it.

Values are typical and drawn from the sources noted. The governing figures are those on your supplier's Certificate of Analysis and the pharmacopoeial monograph you specify.

Mannitol is sold in crystalline, crystallised, spray-dried and granulated grades, each with distinct flow and compaction behaviour. Choosing the grade is a formulation decision, not a commodity purchase.

Crystalline mannitol is used where it will be granulated or dissolved. Spray-dried grades, with their high surface area, compress into stronger tablets than granulated or crystallised grades in dry granulation and roller compaction, according to Merck's technical guide. Particle-engineered direct-compression grades such as Merck's Parteck M, which is 100% beta-mannitol, are designed to give hard tablets that disintegrate quickly and to blend uniformly with micronised actives.

For freeze-drying, buyers usually specify a parenteral-suitable grade. Confirm with the supplier which pharmacopoeial tests are covered for the intended route, such as microbial limits and bacterial endotoxins, rather than assuming a tablet grade is suitable. Chelora Pharmachem lists mannitol in pharma and spray-dried grades.

Mannitol is used mainly as a tablet and capsule diluent, as the base of chewable and orally disintegrating tablets, and as a bulking agent in freeze-dried injectables, with smaller roles as a tonicity agent and plasticiser.

Tablet and capsule diluent

Mannitol is used at 10 to 90% w/w as a diluent in direct compression and wet granulation. Its low hygroscopicity makes it a preferred filler for moisture-sensitive actives, and its chemical inertness reduces the risk of interactions. Merck reports that its directly compressible grade can carry up to 60% of a non-directly compressible active and blend uniformly with micronised actives below 15 µm.

Chewable and orally disintegrating tablets

Its sweetness, cooling sensation and mouthfeel make mannitol a common base for chewable tablets, and its rapid disintegration in directly compressed form suits orally disintegrating tablets. These formats are often paired with a superdisintegrant such as croscarmellose sodium and a lubricant such as magnesium stearate.

Freeze-dried (lyophilised) injectables

As a bulking agent at 20 to 90% w/w, mannitol crystallises during freezing to form a stiff, uniform cake that supports appearance, mechanical strength and reconstitution, and it is generally preferred to glycine for this role.

A 2023 review in the Journal of Pharmaceutical Sciences (Thakral and co-authors) highlights two risks: vial breakage caused by mannitol crystallisation during freezing, and the formation of a metastable mannitol hemihydrate in the final cake. Both need to be managed through formulation and freeze-drying cycle design, including how the frozen solution is held and dried.

Other uses

Mannitol is also used as a tonicity agent, to prevent thickening of aluminium hydroxide antacid suspensions at 4 to 7% w/v, as a plasticiser in soft gelatin capsules and in some sustained-release tablets. In foods it serves as a sweetener, anticaking agent and bulking agent.

Mannitol is non-reducing and non-hygroscopic, while lactose is a reducing sugar that can react with amine drugs. That difference decides most choices between the two common sugar-based fillers.

Lactose monohydrate remains the general-purpose choice for many oral solid doses. Sorbitol, mannitol's isomer, is also used in chewables and liquids, but it is much more hygroscopic, which limits its use in moisture-sensitive solid doses.

Mannitol has monographs in the major pharmacopoeias, is listed as GRAS and appears in the FDA Inactive Ingredient Database for several routes. Its main known effect at high oral intake is a laxative one.

The Handbook of Pharmaceutical Excipients lists mannitol monographs in the British, European, Japanese and United States pharmacopoeias. It is accepted as a food additive in Europe and included in UK-licensed parenteral and non-parenteral medicines. In US foods, 21 CFR 180.25 permits mannitol on an interim basis with maximum levels by food type, and requires the statement "Excess consumption may have a laxative effect" where reasonably foreseeable consumption could give a daily intake of 20 g.

Large oral doses act as an osmotic laxative. Adverse reactions have mainly followed therapeutic intravenous infusions of 20% w/v solutions, and hypersensitivity reactions have been reported with mannitol as an excipient. The WHO has not specified an acceptable daily intake. Hazard classification differs between supplier listings, so rely on your supplier's SDS; the Handbook recommends eye protection because the powder may irritate the eyes.

Mordor Intelligence values the global mannitol market at about USD 498.2 million in 2026, rising to USD 638.03 million by 2031, with pharmaceuticals the fastest-growing application.

This is a single-publisher estimate. Treat it as orientation rather than a contract input.

Seven checks prevent most ordering problems: pharmacopoeia, grade, route, impurities, documents, supply consistency and packaging.

1. 1

   Pharmacopoeia and edition

   Specify USP-NF, Ph. Eur., BP, JP or another required standard, and the current edition.

2. 2

   Grade and polymorph

   State crystalline, spray-dried or granulated, the particle size range and, where it matters, the polymorph.

3. 3

   Route of administration

   For parenteral use, confirm the grade covers the required microbial and endotoxin testing.

4. 4

   Impurities

   Ask for limits on reducing sugars and related polyols such as sorbitol, which matter for sensitive actives and peptides.

5. 5

   Documents

   Request the batch COA, SDS, specification sheet and, where applicable, a Drug Master File reference or regulatory support letter.

6. 6

   Supply consistency

   Confirm the manufacturer, site and grade will stay the same between batches, since a change of source can affect tablet properties.

7. 7

   Packaging and storage

   Confirm lined, sealed packaging and storage in a cool, dry place in a well-closed container.

To discuss a grade or request a sample, send the product name, CAS number, grade, quantity and destination through the contact page. You can also browse the full product list.

Watch pharmaceutical demand, which Mordor Intelligence expects to grow faster than food demand, continued use of orally disintegrating and chewable formats, and growth in freeze-dried biologics that rely on mannitol as a bulking agent.

Because mannitol is made from sugars, feedstock costs and supply also matter. The practical lever for buyers stays the same: specify the pharmacopoeia, grade and route clearly, and keep the source consistent once a formulation is validated.