A drug touted by a small pharmaceutical company as a treatment for Alzheimer’s disease has had a turbulent bid for regulatory approval.

Studies that once seemed to support the drug, simufilam, have been called into question, leading to retractions from scientific journals and resignations of top officials at Cassava Sciences, the company sponsoring it.

In September, the Securities and Exchange Commission brought charges against Cassava Sciences, alleging that the company had made misleading statements about the results of clinical trial data. The S.E.C. also charged a Cassava consultant researcher for manipulating research results.

Cassava Sciences agreed to a $40 million settlement with regulators to resolve the case; the company neither admitted nor denied wrongdoing.

Yet to the consternation of some dementia experts, simufilam remains in advanced clinical trials. “If the efficacy and the underlying data is being questioned, which it is, why would you continue the study?” said George Perry, a neuroscientist at the University of Texas at San Antonio and editor in chief of The Journal of Alzheimer’s Disease, who serves on the boards of companies with other drug candidates.

While some important results have been challenged, the company maintains there are still research and clinical results that suggest the drug may yet prove valuable.