The medicines used to slow mental decline in people with Alzheimer's disease are not particularly effective. When compared with a placebo, only 10 to 20 percent more people taking an Alzheimer's drug seem to benefit at all. And it is the rare person who has a significant delay in the worsening of their symptoms over time.

However, there is no way as yet to predict who will respond and who will get little or no benefit from one of the five drugs approved to treat Alzheimer's disease. Thus, the decision to try one is a gamble and judgment is based on whether the treatment is worth the cost and the risk of side effects.

• Cost. Averaging $148 to $195 a month, the Alzheimer's drugs are costly and may not be worth the added cost if the patient must take many other medicines. This is true even if insurance or Medicare coverage helps pay since out-of-pocket payments can still be quite steep.
• Side effects. While the long-term adverse effects of the Alzheimer's drugs have not been fully evaluated, short-term side effects are either mild or reversible when a person stops taking the medicine. On this basis, many people with Alzheimer's disease may opt to try one of the drugs for six months to a year to see if it helps. We advise close scrutiny of the patient's response by both family and physician.

  Based on the evidence of their effectiveness, side effects, tolerability, flexibility of use, and cost, we have chosen the following as Consumer Reports Best Buy Drugs to treat Alzheimer's disease:

• Donepezil (Aricept) — for people with early-stage Alzheimer's disease
• Galantamine (Razadyne) — for people with early-stage Alzheimer's disease
• Memantine (Namenda) — for people with middle-stage and late-stage Alzheimer's disease

Aricept's and Razadyne's lower risk of adverse effects and higher tolerability justify their choice. We choose Namenda because it is the only drug approved by the Food and Drug Administration to treat people with middle- to late–stage Alzheimer's disease. It also acts differently in the body than the other drugs, and because of that can be taken in addition to them. That could be an advantage, but we caution that studies have not yet conclusively established whether such combination treatment is better than treatment with one drug alone.