Here, we describe the cocrystallization of the trypanocide drug diminazene with the macrocyclic host cucurbit[6]uril (CB6). When the acid-contaminated CB6 was used, diminazene and the product of its hydrolysis cocrystallized with CB6. The use of an acid-free macrocycle afforded a host–guest complex where diminazene guest molecules are complexed exo to the host cavity.