On August 16, 2016, the US food and drug administration ([https://www.fda.gov/ FDA]) published a draft guidance [https://www.fda.gov/files/drugs/published/Regulatory-Classification-of-Pharmaceutical-Co-Crystals.pdf Regulatory Classification of Pharmaceutical Co-Crystals]. In this guide, the FDA suggests treating co-crystals as polymorphs, as long as proof is presented to rule out the existence of ionic bonds.