hard gelatin capsule

A hard gelatin capsule is the classic two-piece shell that looks like a tiny coloured barrel: a longer body and a shorter cap that slide together and snap shut, like the two halves of a toy Easter egg. You pour a dry fill into the body, push the cap on, and the dose is sealed.

The shells are made by dipping cold metal pins into warm gelatin solution, drying the film, and cutting the cap and body to size. They are filled mostly with powder or granule blends, though pellets, mini-tablets and even semi-solids can be used. Standard sizes run from large (00 or 000) down to small (5), letting the formulator match shell volume to the dose. After filling, the two pieces may be locked or band-sealed to stop them springing apart.

Because the contents are dry, hard capsules suit a wide range of drugs and are popular for clinical trials, where a blank shell can disguise a tablet for blinding. Their main weak point is that gelatin softens in heat and high humidity and can become brittle when too dry, so storage conditions matter.