What matters in this format
Hard capsules suit powders and granules that compress poorly, react to heat or pressure, or taste unpleasant. The limiting factor is volume. Each shell holds a fixed fill volume, so the bulk density of the blend, not its mass, decides how much active fits. Five points decide whether a fill works.
- Fill volume and density. Light, fluffy powders reach the volume limit before the target mass. Dense salts allow more milligrams per shell.
- Flow. Dosator and tamping-disc machines need a blend that flows evenly into the dosing station. Poor flow causes fill-weight variation and failed uniformity checks.
- Moisture and shell compatibility. Gelatin shells hold water as a plasticiser. Hygroscopic fills draw that water out and make shells brittle, while wet fills soften them.
- Reactivity. Gelatin can cross-link with aldehydes and other reactive fill components, especially under heat and humidity. Cross-linked shells dissolve more slowly, so plan dissolution testing on stability samples.
- Low-dose uniformity. Micrograms of a vitamin spread through hundreds of milligrams of blend need a diluted grade and a validated mixing step.
Liquids and oils need banded or sealed hard capsules, or a different format. See ingredients for softgels.
Ingredients that suit it
| Ingredient type | Examples | Why it fits capsules | What to watch |
|---|---|---|---|
| Low-dose vitamins | cholecalciferol (vitamin D3), cyanocobalamin, folic acid | Tiny mass per serving, no compression stress | Use diluted grades; confirm blend uniformity; protect light-sensitive vitamins |
| Botanical and polyphenol extracts | curcumin, quercetin, resveratrol | Shell hides colour and taste; no compression needed | Low bulk density limits fill mass; curcumin stains equipment |
| Enzymes | bromelain, papain | Avoids the heat and pressure of tableting | Activity loss with moisture and heat; enzyme dust needs containment |
| Sulphur-containing actives | N-acetyl-L-cysteine, glutathione | Shell masks the sulphurous odour | Oxidise in air and moisture; tight packaging |
| Hygroscopic actives | L-carnitine | Avoids sticking to tablet punches | Absorbs moisture readily; prefer HPMC shells and low-humidity filling |
| Mineral salts | magnesium oxide, calcium carbonate | High elemental content per gram keeps fill mass down | High label claims may need more than one capsule per serving |
| Powdered coenzymes | coenzyme Q10 | Powder grades fill like other actives | Light sensitive; oil-based grades suit softgels |
For hygroscopic carnitine, the salt forms on the carnitine forms page are usually easier to handle than the base. For minerals, work out fill mass per serving with the elemental content calculator before fixing the capsule size. The magnesium forms guide compares salts by elemental content. Vitamins that degrade over shelf life need an overage, which the overage calculator handles.
The specification sheet sent with each quote states the density and particle-size parameters where they apply. Ask for the grade that matches your filling machine in the quote form.
Excipients and processing aids
The shell material is the first choice, because it sets the moisture conditions for everything inside it.
| Shell material | Origin | Moisture behaviour | Usual reason for choosing it |
|---|---|---|---|
| Gelatin | Animal collagen | Relies on bound water; brittle when dried, soft when humid | Established, fast to fill, wide machine compatibility |
| HPMC (hypromellose) | Cellulose derivative | Lower water content; tolerates hygroscopic fills | Non-animal positioning; hygroscopic or moisture-sensitive fills |
| Pullulan | Microbial fermentation polysaccharide | Non-animal film with low oxygen permeability | Oxygen-sensitive fills; transparent shells |
Gelatin species matters to brands with dietary or religious requirements. Specify the source you need when you ask for a quote.
Fill excipients make the active run on the machine and reach the target fill weight.
| Excipient | Role | What to watch |
|---|---|---|
| Microcrystalline cellulose | Filler and diluent; bulks out low-dose blends | Choose a grade that matches the active’s particle size to limit segregation |
| Mannitol | Filler | Non-hygroscopic, so it suits moisture-sensitive blends |
| Silicon dioxide | Glidant and anti-caking agent | Small additions improve flow; it also adsorbs moisture and oils |
| Magnesium stearate | Lubricant; reduces sticking to dosators | Over-mixing makes the blend hydrophobic and can slow dissolution |
The other excipients in the Excipients & Processing Aids category serve other formats. Pectin, sorbitol and erythritol belong in gummies. Citric acid and trisodium citrate are acidulants and buffers in effervescent tablets, and polydextrose bulks powders.
Regulatory and labelling points
Directive 2002/46/EC defines food supplements as products marketed in dose form and names capsules among those forms. Vitamins and minerals in the fill must be in forms listed in Annex II of the Directive. The permitted forms guide explains how to check a form.
Shell polymers and fill excipients used as food additives must be authorised for food supplements in Annex II of Regulation (EC) No 1333/2008. They must also meet the specifications in Regulation (EU) No 231/2012. Gelatin is a food ingredient, not an additive. Titanium dioxide is no longer an authorised food additive, so opaque shells need another opacifier or colour system.
Under Regulation (EU) No 1169/2011, the shell components are ingredients and belong in the ingredients list. Additives are declared by functional class followed by their specific name or E number. The labelling guide covers the mandatory food-supplement particulars.
At the time of writing, the EU has no harmonised legal definition of “vegetarian” or “vegan” for food labels. Check national guidance before using these terms on HPMC or pullulan capsules. Maximum amounts of vitamins and minerals are also set nationally; see maximum levels by EU country. Unusual shell materials or fill ingredients may fall under the novel food rules, covered in the novel food guide.