4‑Aminosalicylic Acid Adducts

4-Aminosalicylic acid (<i>p</i>-aminosalicylic acid, PAS), an antituberculosis drug, is a model active pharmaceutical ingredient to study salt and cocrystal formation in a multiple hydrogen-bonding functionality molecule with carboxylic acid, amine, and phenol groups. A cytosine salt CYT<sup>+</sup>–PAS<sup>–</sup>, salt cocrystal hydrate CYT<sup>+</sup>–PAS<sup>–</sup>–CYT–H<sub>2</sub>O, and nicotinamide cocrystal hydrate PAS–NAM–H<sub>2</sub>O, are described in this article. Furthermore, X-ray crystal structures of PAS sodium dihydrate, sulfate, and mesylate salts and dehydration/rehydration behavior of the sodium salt by powder X-ray diffraction are discussed.