Adverse effects of antiepileptic drugs (AEDs) are common, can have a considerable impact on quality of life and contribute to treatment failure in up to 40% of patients. The adverse effect profiles of AEDs differ greatly and are often a determining factor in drug selection because of the similar efficacy rates shown by most AEDs. The most common adverse effects are dose dependent and reversible. Cognitive impairment is of particular concern, especially for patients who work or study. Idiosyncratic effects, such as skin rashes, and chronic effects, such as weight gain, can lead to high rates of treatment discontinuation and complicate clinical management. Nearly all conventional AEDs increase the risk of congenital malformations when taken during pregnancy, with valproate posing a potentially greater risk, whereas the potential teratogenicity of new generation AEDs is largely unknown. Most conventional AEDs have a poor record when it comes to drug interactions, largely because of their tendency to interfere with hepatic drug metabolism. Some newer AEDs have no effect on hepatic drug metabolizing enzymes and are renally excreted, resulting in a lower potential for drug interactions. However, further research is needed to confirm the apparent improvement in tolerability offered by some of the newer AEDs.