Proper characterization of pharmaceutical products with respect to particle size and distribution requires that the extent and size of drug particle agglomerates is determined, as well as the size and number of primary Active Pharmaceutical Ingredients (API) particles. Such characterization may also be necessary for assessing product quality, establishing Bioequivalence (BE), evaluating out-of-specification issues, batch-to-batch comparison studies and addressing stability of the product during scale-up, and long-term shipping/storage in varying environmental conditions. By providing chemically specific identification for each particle in addition to Particle Size Distribution (PSD), Raman Chemical Imaging (RCI) is an effective tool for identifying whether observed aggregates/agglomerates are combinations of multiple primary API particles, API-excipient particles or multiple excipient particles. In concert with other particle sizing techniques, RCI analysis of agglomerates can benefit developers of Orally Inhaled and Nasal Drug Products (OINDPs), containing multiple APIs and/or excipients such as nasal suspensions, dry powder inhalers and metered dose inhalers.