In 2003, researchers gave ginkgo extract to a special strain of mice that produce abnormally large amounts of beta-amyloid precursor protein and are known to experience age-related cognitive problems, beta amyloid plaque accumulation, and oxidative stress. The mice were split into two groups, one with free access to ordinary water, and one with access to water that had been infused with ginkgo extract. After 10 days, the mice were given a spatial memory test. The impaired mice who had been drinking ordinary water performed poorly on the test, while those who had been drinking ginkgo extract performed exactly the same as healthy mice.
Also in 2003, researchers from the University of Southern Mississippi investigated ginkgo's antioxidant properties in a worm model of Alzheimer's as well as in cell cultures. Both the worms and the cell cultures had been altered in a way that caused them to produce and accumulate increased amounts of beta-amyloid plaque, which also led to an increase in reactive oxygen species. Using ginkgo extract reduced the excess ROS. Two years later, the same team of researchers investigated the mechanisms behind ginkgo's neuroprotective effects. They found further evidence to support their previous findings about ginkgo's ROS-fighting abilities, and also reported that it can inhibit the formation of plaques and reduce plaque-related toxicity.
A 2006 study compared ginkgo extract to a placebo and to donepezil, a common Alzheimer's medication. At the end of a 24-week trial, ginkgo and donepezil had similar levels of efficacy in terms of their ability to slow disease progression and improve cognition.
Researchers have reported mixed results in studies using ginkgo extract, so this treatment may be more effective for some people than others.