Cocrystals of carbamazepine with nicotinamide and saccharin are shown to be polymorphic. Two polymorphs of carbamazepine-nicotinamide (CBZ-NCT) cocrystals and two polymorphs of carbamazepine-saccharin (CBZ-SAC) cocrystals were grown from solution in the presence of polymer heteronuclei. The two CBZ-NCT polymorphs, CBZ-NCT I and a polymer nucleated (PN) form of CBZ-NCT, were characterized by Raman spectroscopy and powder X-ray diffraction. CBZ-SAC II, a new polymorph, was found to be in the monoclinic space group C2/c with a = 35.72 Å, b = 6.84 Å, c = 16.11 Å, and β = 98.03°. The unique feature of CBZ-SAC II is the formation of a heterosynthon between the carbamazepine and saccharin. These results are notable because CBZ-NCT and CBZ-SAC are among the most widely studied pharmaceutical cocrystals.