Lamictal (lamotrigine) is approved by government regulatory agencies in most countries for adjunctive (add-on) therapy for partial seizures in adults whose seizures are not well controlled by other medications. Randomized, controlled studies of Lamictal used in this way have found that Lamictal reduces seizure frequency by at least half in 16% to 20% more patients than a placebo. Side effects were more troublesome than with the placebo, but they were generally minor and often went away without stopping the medication.

Lamictal is also used to treat absence, myoclonic, and tonic-clonic seizures. It is effective against some seizure types in patients with Lennox-Gastaut syndrome and other forms of symptomatic generalized epilepsy. In one study using Lamictal as add-on therapy for patients with Lennox-Gastaut syndrome, 23% more patients who took Lamictal (compared to a placebo) had the number of their tonic-clonic seizures cut at least in half. Nearly half of the patients who took the Lamictal had less than a 25% decrease in these seizures, however.

No single combination of antiepileptic medications is perfect for everyone. Sometimes a series of combinations must be tried before finding what is best for the individual. Many seizure medicines affect the way the body metabolizes Lamictal, so the dosage must be adjusted if it is given as add-on therapy in combination with these medications.

Studies have also looked at the effectiveness of Lamictal used alone. In one study, patients with newly diagnosed epilepsy were treated with either Lamictal or carbamazepine (Tegretol, Carbatrol). A similar study compared Lamictal to phenytoin (Dilantin, Phenytek). The patients in these studies had partial seizures with or without secondary generalization, or they had primary generalized tonic-clonic seizures. In each study, the effect on the frequency of each seizure type was almost the same for both medications, but the patients taking Lamictal had fewer problems with side effects.