Common side effects include nausea, insomnia, tiredness, back pain, runny nose (rhinitis), mild rash, abdominal pain, dry mouth, constipation, vomiting, cough, and sore throat.
Serious, but very rare, side effects include life-threatening skin rashes (Stevens-Johnson syndrome and toxic epidermal necrolysis). This risk of serious rash is decreased by slowly increasing the medication to its recommended dosage and avoiding combining it with other medications known to cause this reaction, such as valproic acid (Depakote). That said, there are studies that have used lamotrigine in combination with valproic acid for the treatment of bipolar disorder. Also, while much attention has been paid to this rare but serious adverse reaction, it’s important to remember that many other medications, including commonly prescribed antibiotics, are far more likely to cause this reaction.