Eli Lilly and Company has halted development of a potential treatment for Alzheimer's disease after preliminary results from two studies showed it worsened the conditions of some study subjects.

The pharmaceutical company, maker of semagacestat, made the announcement on Tuesday.

Preliminary results of Phase III studies involving 2,600 patients with mild to moderate Alzheimer's found those on semagacestat were worse off in congition and ability to perform daily tasks than those on placebo.

The company is telling clinical trial investigators to contact study participants, including those in Canada, as soon as possible to tell them to immediately stop taking the study drug.

The U.S. National Institutes of Health's clinical trial website lists study locations in B.C., Manitoba, Ontario and Quebec.

The drug was designed to reduce the body's production of amyloid beta plaque, thought to play a role in causing Alzheimer's.

Lilly said the decision did not affect the ongoing clinical trials of solanezumab, its other drug in Phase III study under development also for Alzheimer's.

Alzheimer's is a fatal form of dementia that causes progressive decline in memory and other aspects of cognition.

It is the most common form of dementia and affects one in 20 Canadians over 65 — about 290,000 people. The number rises to one in four in those over 85.