Does the drug work immediately?
No, the effects of memantine take time. Experts claim that it takes an average of 2-3 weeks to see full benefits of the drug. If the drug has not worked at the end of 4 weeks, it is unlikely to work at all. One can always increase the dosage, but you also increase the incidence of side effects.
So what does all this mean?
Memantine does have a mild beneficial effect at 6 months in patients with moderate to severe AD. In individuals who have early or mild AD, there is no benefit. From the many patient testimonials (which are more honest than what the company claims) on cyberspace, Memantine does appear to show very mild benefits in less than 5% of patients with AD. The majority of testimonials on memantine claim that the drug does nothing and a few patients had to discontinue the drug because of side effects. Many patients found no change after months of taking memantine.
Of more importance is the fact that memantine is one of the most expensive drugs around. Each tablet costs anywhere from $2.-$3. You take two pills a day and that averages to about $120-$180 a month. Moreover, there is zero guarantee that the drug will work. In Britain, the UK National Institute for Clinical Excellence has voted against the use of this drug on grounds that its high cost outweigh any benefits - I wholeheartedly agree.
http://www.cochrane.org/reviews/en/ab003154.html