Mood effects of antiepileptic drugs

This article reviews our knowledge about a specific subgroup of chronic CNS-related side effects of antiepileptic drugs (AED) treatment, i.e., the effects of AEDs on mood. In line with a recent hypothesis, using the experience of AED treatment in psychiatry, we examined whether mood effects are related to the known anticonvulsant mechanisms of action of the AEDs. Specifically we examined whether AEDs, acting through potentiation of GABAergic neurotransmitter release, have "sedating" effects on mood, whereas AEDs that act through the reduction of excitatory glutamate neurotransmitter release have "activating" effects on mood. The results of this review yield evidence that there are relationships between the known anticonvulsant mechanisms of action of the AEDs and mood effects. Mood effects occur especially when the drugs have a sustained effect on neuronal mechanisms, in particular when the inhibitory or excitatory neurotransmitter release is altered. Drugs with "use-dependent" impact on sodium or calcium channels probably have a more transient impact and do not lead to interictal stable mood effects. Drugs with multiple mechanisms of action seem to combine a favorable efficacy profile with an increased risk of severe mood problems. The quality of the evidence, however, is not conclusive and there are many paradoxical results. One reason for this lack of "fit" may be the use in this review of a simplified classification, based only on the predominant mechanism of action to classify a drug. Only a limited number of AEDs (ethosuximide, tiagabine) are characterized by a single anticonvulsant mechanism of action. Probably more detailed coupling of mechanisms of action (e.g., inspecting the type and route of impact on GABA release) and mood effects may give less confusing results. The use of magnetic resonance imaging techniques such as spectroscopy may provide interesting results.