A once-promising Alzheimer’s drug did not help patients remember better or think more clearly, and the company said Wednesday it had dropped plans to market it for people with mild dementia.

The drug, called solanezumab, was designed to clear the brain-clogging amyloid plaques that are one main physical symptom of Alzheimer’s. But patients with early dementia due to Alzheimer's didn’t seem to get much benefit from the drug, the company that makes it said.

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“Patients treated with solanezumab did not experience a statistically significant slowing in cognitive decline compared to patients treated with placebo,” drug maker Eli Lilly and Co said in a statement.

“Lilly will not pursue regulatory submissions for solanezumab for the treatment of mild dementia due to Alzheimer’s disease.”

“Patients treated with solanezumab did not experience a statistically significant slowing in cognitive decline compared to patients treated with placebo."

It’s a terrible blow for Alzheimer’s researchers, patients and their family members.

More than 5 million Americans have Alzheimer's disease. The Alzheimer's Association says more than 28 million baby boomers will develop the disease between now and 2050.

Related: Dementia Rates Might be Declining

Just this week, researchers reported that dementia rates appeared to be falling in the U.S. But the number of people reaching age 65 and at higher risk of dementia is growing, so even if rates fall, the number of people with Alzheimer’s and other forms of dementia can still grow.

There are just a handful of Alzheimer's drugs on the market now, all approved more than a decade ago. They include Aricept, Namenda and Exelon, and they can treat symptoms for a while but do not affect the disease itself.

Companies have been betting on a new generation of “magic bullet” drugs -- solanezumab, aducanumab and gantenerumab. They are engineered proteins that specifically attack amyloid.

“While today’s results are a setback for the amyloid hypothesis, there are several other anti-amyloid drugs still in clinical trials that work in different ways."

“The results of the solanezumab EXPEDITION3 trial were not what we had hoped for and we are disappointed for the millions of people waiting for a potential disease-modifying treatment for Alzheimer’s disease,” said John Lechleiter, president and chief executive officer of Lilly.

“We will evaluate the impact of these results on the development plans for solanezumab and our other Alzheimer’s pipeline assets.”

Related: New Alzheimer's Drugs Offer Exciting Possibilities

One bit of good news – the drug did not seem to cause severe side effects. Some Alzheimer’s drugs have caused dangerous and even fatal brain swelling.

Solanezumab has been showing disappointing results since 2012. But the developers kept studying it, trying to see if it maybe offered a small benefit when given to people early.

Related: The Race for the Next Generation of Alzheimer's Drugs

“Solanezumab is designed to mop up amyloid protein – a key hallmark of Alzheimer’s – and is the result of years of development based on the concept that this protein is a central driver of the disease,” said Dr. David Reynolds, Chief Scientific Officer at Alzheimer’s Research U.K.

“While today’s results are a setback for the amyloid hypothesis, there are several other anti-amyloid drugs still in clinical trials that work in different ways, some of which are being tested even earlier in the disease process than solanezumab. We can’t disregard these ongoing trials and their findings will now be more important than ever in shaping the search for disease-modifying treatments for Alzheimer’s."