Another Alzheimer’s drug has—mostly—fallen short of researchers’ expectations, drug developer TauRx said in a statement July 27.

The medicine was intended to untangle one of the types of protein clusters that characterize Alzheimer’s disease patients’ brains. Many previously studied Alzheimer’s drugs are designed to perform similar functions on amyloid proteins in the brain, though this drug, called LMTX, focused on tau proteins.

According to a company statement, the drug failed to meet phase 3 co-primary endpoints over the 15-month study. It was not useful in slowing or reversing cognitive or functional impairment or brain atrophy in most of the 891 participants, especially the ones who were already taking a first-line drug before the study. LMTX failed in its goal to be a second therapy intended to boost the effects of existing drugs.

On the other hand, the drug did show  a “clinically meaningful” ability to impede disease progression in patients with mild to moderate Alzheimer’s who were not already taking another Alzheimer’s medication. But the patients who took only LMTX only made up 15 percent of the trial, so it’s difficult to get a full picture of its potential at this time, the drug maker said.

“[T]hese results support the targeting of the tau tangle pathology in Alzheimer's disease as being a very promising drug development pathway,” TauRx cofounder Claude Wischik said in a statement. "However, the reason for the observed loss of efficacy of LMTX when taken in combination with currently available treatments for Alzheimer's disease is not as yet understood." 

At the Alzheimer’s Association International Conference, where the results were presented, Wischik said these cognitive improvements are as high as 85 percent, NBC News reported.

But according to Forbes, experts outside the company are less optimistic about what this means for the drug. One Mayo Clinic neurologist emphasized the unreliability of secondary results. And since the secondary results were not as rigorously examined, they might not hold up in future trials, one Alzheimer’s Association scientist said.