Primidone is a barbiturate-type anticonvulsant used therapeutically for over 50 years in the management of focal, psychomotor, and grand mal seizures. It acts mechanistically by decreasing neuron excitability, thereby raising seizure thresholds. Primidone is available by prescription under the trade name Mysoline® and several other trade names, and it has a pregnancy category classification of D. Animal studies with primidone are limited. A number of additional studies recorded malformations resulting from primidone in combination with other anticonvulsants; the combination of valproic acid, carbamazepine, and primidone is considered by some the most risky of all regimens. In a small number of reports, researchers did not find primidone-induced malformations with or without combined drug therapy. Primidone is an average-sized molecule that is slightly hydrophilic. It is of average polarity in comparison to the other human developmental toxicants. Primidone can engage in hydrogen bonding both as an acceptor and donor.