Praziquantel (PZQ) is widely used to treat schistosomiasis. However, this chiral pharmaceutical is still produced as a racemic compound (both enantiomers crystallize together in the crystal lattice) while only the R enantiomer is active. A possible way to control the solid properties of chiral APIs and herewith to separate the enantiomers is their co-crystallization with a coformer, either to form a salt or a co-crystal. The crystallization behavior of such systems is still not well-understood. For instance, the nucleation rate of such co-crystals can be low compared to the nucleation rate of pure components and therefore, co-crystal nucleation can require a higher driving force. A previous co-crystal screening has identified vanillic acid (VA) as a coformer able to form two different co-crystals with PZQ.1 Further analysis shows that these two co-crystals exist at different molar ratios: PZQ:VA crystallizes as racemic compound and PZQ:VA2 is a conglomerate. The phase diagram of this system has been established to identify the thermodynamic stability and the solubility of the different solid forms. This system offers the opportunity to study the crystallization kinetics using the probability distribution of induction times2 of the racemic compound and the conglomerate co-crystals in comparable conditions, as the same components are involved. The crystallization kinetics of the conglomerate co-crystal are much slower than those of the racemic co-crystal compound, perhaps due to self-poisoning in the conglomerate. The comparison of the crystallization behavior of these different solid forms should lead toward an improved understanding of the crystallization behavior of co-crystals as well as racemic compounds and conglomerates.