Imagine a drug that failed to meet basic targets set by the FDA, came with a higher risk of side effects than its predecessors, and was found to be so unimpressive and even dangerous that the agency's own experts advised against approving it.

Now, stop imagining -- and just take a look at Aricept 23, because an explosive new analysis in BMJ says that's exactly how this drug reached the market.

How did it happen? Let me back up to 2010, when the original Aricept -- a drug that did up to $2 billion a year in sales -- was about to lose its patent protection.

Once cheap generics flood the market, it's usually the end of the line for the money train -- unless you have a few tricks up your sleeve, like what the industry calls "evergreening."

That's a slight tweak to help extend the drug's profitable life. It might be a timed-release formula, the addition of a second drug to the mix, or even a change to the dosage itself -- and when the FDA signs off on it, the "new" drug gets three more years of protection.

In this case, it was a change to the dose. While "old" Aricept had been approved in 5 mg and 10 mg doses, Aricept 23 is -- as the name implies -- 23 milligrams of the drug.

The feds said this high dose would be approved only if it beat the lower doses in two key areas: overall cognition and global functioning.

That shouldn't have been too hard, since the old formula was thoroughly unimpressive itself. But Aricept 23 offered only tiny improvements in cognition and no changes at all in the more important measure of global function -- and came with a higher risk of nausea and vomiting as well.

Those side effects are bad enough for a healthy person. But for an Alzheimer's patient, they could be dangerous and even deadly.

No matter. An agency bigwig went against the advice of his own experts and approved the drug anyway -- just four months before the expiration of the original Aricept patent.

Since the generics would only be available in the old 5 mg and 10 mg doses, even a combination of pills wouldn't add up to the "new and improved" dose. The only way to get it was to keep buying the expensive brand-name version.

In other words, the new formula of Aricept didn't protect dementia patients from the ravages of the disease -- but it did protect the profits of the drug's makers, with three years of fresh patent protection.