Memantine is licensed for the treatment of moderate to severe AD. As an NMDA receptor antagonist, it blocks the effects of pathologically elevated glutamate levels. Memantine is available as tablets or an oral solution. The starting dose is 5mg once daily for a week, increasing by 5mg at weekly intervals up to a maximum of 20mg. The most common adverse effects include headache, constipation, sleepiness, dizziness, balance disorders, hypertension, breathlessness and elevated liver function tests. Memantine should be avoided in severe hepatic impairment and used with caution in patients with a history of seizures or renal impairment.