with PVP and P(VP-co-VA). Besides showing the existence of several interactions of the carboxylic acid moiety of IND in the ASD, including the carboxylic acid hydrogen of IND binding to the PVP carbonyl and/or vinyl acetate carbonyl of P(VP-co-VA), they showed that with increasing polymer content, the signal displaying the IND carboxylic acid dimers decreases, which is in line with our observations for the IND-P1 / IND-P2 ASDs (Figure , Supporting Information Figure ). At the same time, the signal attributed to the carboxylic acid-amide complex increases and gradually dominates the spectrum. For the samples containing P1 or P2 this manifests as the observed shoulder of signal 4 at approximately 172 ppm. Additionally, Yuan et al. observed that both polymers, PVP and P(VP-co-VA), in general showed the same behavior regarding hydrogen bonding with IND. However, the hydrogen bond accepting capability of the polymers differed. Due to the lower content of tertiary amides in P(VP-co-VA) compared to PVP, fewer carboxylic acidamide complexes can form in the ASD, which is in line with the observations that the signal attributed to the IND carboxylic acid dimer is more intense for P(VP-co-VA) than for PVP in ASDs with the same drug loading. As indomethacin dimers with cyclic hydrogen bonding between the carboxylic acid moieties are present in both IND polymorphs, α-and γ-, carboxylic acid dimer formation is probably a critical step in the crystallization process from drug-polymer mixes. It should be noted that the dimers described by Strachan et al. in amorphous IND might serve as nucleation points for crystallization. Also Yuan et al. hypothesized that the absence of drug-drug dimers or the inhibition of dimer formation in an ASD due to polymer-drug hydrogen bonding, could effectively inhibit the recrystallization of the drug in the ASD at room temperature and therefore benefit the stability of the amorphous form of the drug. A similar hypothesis regarding the stability of polymer-drug mixtures between PVP and IND was suggested by Matsumoto et al.