By Meera Senthilingam, CNN

Updated 3:02 PM ET, Fri December 9, 2016

(CNN) The results of recent trials that tested much-anticipated Alzheimer's disease drugs dashed the hopes of patients with the debilitating condition. The most recent disappointment came from the large trial for solanezumab, by Eli Lilly, announced last month.

But experts across the field say hope is not lost. They believe we will have some form of drug against the disease by 2025, albeit most likely a pilot version that will need to be upgraded.

This target, in less than a decade, is the goal set by world leaders at the G8 dementia summit in 2013.

Researchers believe there are enough competitors in the race to get at least a few to the finish line on time.

"There are still a number of late-stage trials in progress," said Heather Snyder, senior director of medical and scientific operations at the Alzheimer's Association. "2025 is a realistic target in terms of where we are with the science. ... We're not off-track at this point in time."

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Twenty-four drug candidates are currently in phase 3 trials on humans -- trials that involve larger numbers of people and a comparator to see a drug's true effect -- and many more potential drugs are in earlier stages of development. Speaking from the Clinical Trials on Alzheimer's Disease conference in San Diego this week, Snyder is hopeful that a few drug options -- not just one -- may surface to one day treat Alzheimer's at various stages of the disease.

The question now is, which trials will they be? Unlike with many other diseases, scientists don't fully understand the underlying causes of Alzheimer's, meaning drugs now in development are targeting different aspects of what is theorized to cause symptoms.

"This is a complex disease," Snyder said. "If you think of HIV or cancer ... we don't treat those diseases with one drug." The end result may have to be a combination therapy.

It's estimated that 46.8 million people were living with dementia worldwide in 2015, of which Alzheimer's disease is considered to be the leading cause. More than 5 million people are living with the condition in the United States.