soft gelatin capsule

A soft gelatin capsule, or softgel, is a single sealed bubble of flexible shell with a liquid or oil sloshing inside — picture a tiny squishy water balloon you can swallow. Because the shell is one continuous piece with no join to pull apart, the liquid fill stays sealed in until the shell dissolves.

Softgels are formed and filled in one step: two ribbons of gelatin (made flexible by added plasticiser such as glycerol) pass between rotating dies that simultaneously cut, fill and heat-seal each capsule. The fill is usually a drug dissolved or suspended in oil or another non-aqueous liquid. Presenting a drug already in solution can give faster, more consistent absorption and lets you dose drugs that are oily or very low in melting point.

The downsides are a more complex, costly manufacturing process and limited compatibility: water and water-loving solvents would dissolve the gelatin from the inside, so fills must be carefully chosen. Heat and humidity during storage can also distort the soft shell.