amorphous solid

If a crystal is like neatly stacked oranges in a crate, an amorphous solid is like the same oranges dumped in randomly. The molecules are frozen in place but with no long-range repeating order, more like a very stiff liquid that has been caught mid-pour. Glass is the everyday example, and many drugs can be coaxed into a glassy, amorphous state.

Because its molecules are disordered, an amorphous solid has no crystal lattice to break apart, so dissolving it costs less energy than dissolving the crystal. The result is often markedly higher apparent solubility and faster dissolution, which is a major advantage for poorly soluble drugs. Amorphous forms are produced by methods such as rapid cooling of a melt, spray drying, or freeze drying.

The catch is that the amorphous state is thermodynamically unstable: it sits at higher energy than the crystal and tends to crystallize over time, especially when exposed to heat or moisture. If it recrystallizes, the solubility gain is lost. So amorphous drugs are usually not used neat but are stabilized, most often by dispersing the molecules in a polymer to hold them apart and slow crystallization.