melting point

The melting point is simply the temperature at which a solid gives in to heat and turns to liquid — like an ice cube becoming water, but for a drug crystal. At that temperature, the orderly lattice has absorbed enough thermal energy that its molecules break free and start to flow.

For a crystalline drug the melting point is a useful identity and purity check. A pure crystalline substance melts sharply over a narrow range; impurities or a different solid form depress and broaden the melt, so a low or smeared melting point is an early warning sign. Different polymorphs of the same drug have different melting points because their lattices hold together with different strength.

Melting point also carries practical formulation meaning. A very high melting point often signals a strong, stable lattice and lower solubility, while a low melting point can mean sticky behavior during milling and compression or even partial melting from process heat. It is routinely read off a differential scanning calorimetry trace as a sharp endothermic peak, alongside other thermal events.