When sourcing Phenibut (4-amino-3-phenylbutyric acid), the primary indicator of quality is purity, which should be ≥99% as verified by HPLC (High-Performance Liquid Chromatography). Buyers must distinguish between Phenibut HCL (Hydrochloride), which is highly soluble and crystalline, and Phenibut FAA (Free Amino Acid), which is closer to neutral pH and suitable for sublingual use. Ensure the Heavy Metal content is <10ppm and Microbial counts meet USP or EP standards to ensure safety for end-consumers.