A treatment for Alzheimer's failed to slow mental decline in a widely anticipated study, ending hope that researchers at by Eli Lilly had finally found a drug that does more to help those suffering from the fatal, mind-robbing disease.

The pharmaceutical company's shares plunged 14 percent Wednesday before markets opened.

The drug, solanezumab, missed the study's main goal when patients taking it did not experience a statistically significant slowing of cognitive decline — which involves a person's ability to remember things — compared to those taking a placebo or fake drug.

Solanezumab also had failed in two previous large studies of people with mild-to-moderate forms of the disease, but combined results suggested it might slow decline for those with the mildest symptoms. Lilly then decided to start another study focused on those patients.

Alzheimer's is a degenerative, fatal disease that impairs memory and thought. It is characterized by the buildup in the brain of a protein called amyloid beta that clumps together to form sticky plaques between nerve cells. More than 5 million people in the United States have Alzheimer's, the most common form of dementia.

It is the sixth-leading cause of death in the United States and the only one without a way to prevent, cure or even slow its progression, according to the Alzheimer's Association.

Solanezumab (sol-ah-NAYZ-uh-mab) is delivered intravenously and binds to the amyloid protein to clear it from the brain before it clumps together forming plaques.

Some researchers think the proteins trigger Alzheimer's before they form the plaques, but they aren't certain yet whether those proteins or the plaques are a cause of the disease, or if they're just a symptom. Other companies are testing drugs in an attempt to remove the protein.

Alzheimer's experts had modest expectations for Lilly's latest study, in part because a statistically significant result — which means a change is likely not due to random chance — doesn't necessarily deliver a dramatic improvement in how patients live with the disease.

But a positive result would have been better than what is out there now. Current Alzheimer's treatments like Aricept and Namenda only temporarily ease symptoms such as memory loss, confusion and agitation. They don't slow, stop or reverse the mental decline that happens when the brain's nerve cells stop functioning normally.

Many Alzheimer's patients typically live an average of eight years after their symptoms become noticeable, as the disease gradually erodes their memory and ability to think or perform simple tasks.

At least 18 other drugs are in late-stage testing, including several similar to solanezumab.

Shares of Indianapolis-based Eli Lilly and Co. shares tumbled $10.72 to $65.27 in premarket trading.