The medications used to treat mental decline in people with Alzheimer's disease are not particularly effective. When compared to a placebo, most people who take one will not experience a meaningful benefit. And once taken, it is rare for a person to experience a notable delay in the worsening of their symptoms over time. (The medications do not treat Alzheimer's disease directly, only its symptoms.)

Yet, there is no way to predict who will get a benefit from one of the five drugs approved to treat Alzheimer's disease and who will not. So the decision to try an Alzheimer's medication should be based on whether any potential benefit is worth the cost, and the risk of side effects.

• Cost. Averaging about $177 to more than $400 per month, the Alzheimer's disease drugs are costly and may not be worth it if a person takes many other medications for other health conditions. This is true even if insurance or Medicare coverage helps pay since out-of-pocket payments can still be quite steep.
• Side effects. One of the Alzheimer's medications, tacrine (Cognex), poses a risk of liver damage, so it is now prescribed only rarely. The four other drugs can cause several side effects. Most are minor, such as nausea, vomiting, dizziness, loss of appetite, muscle cramps, tremor, and weight loss. But for some people, these adverse effects might persist or be intolerable. These medications can also pose more serious side effects in rare cases, such as a slow heart beat, heart block, gastrointestinal bleeding and ulcers, and possibly convulsions or seizures.

Because most people who take an Alzheimer's medication will not experience a useful benefit, together with the relatively high price tag and the risk of rare but important safety concerns, we are unable to choose any of these drugs as a Best Buy.

However, we realize that many people will want to try one of these medications if they, or somebody they care for is suffering from Alzheimer's disease. In that case, it makes sense to try one that has the lowest rate of side effects and is the least expensive since none of the medications has been shown to be more effective than the others.

In that case, generic donepezil or generic galantamine meet both criteria. Both have a lower risk of adverse effects and higher tolerability than the other medications, and since they are generic, their price is much less than the brand-name medications.

But if the person taking the drug does not show signs of improvement within three months, it is unlikely that they ever will, so the drug should then be stopped.

This report was updated in June 2012.