What’s behind the Viagra and Alzheimer’s study?

“Viagra may help reduce Alzheimer’s risk, according to a new study,” reported Fortune.com in February. Really?

UK scientists examined the health records of 269,725 men aged 40 or older who had a new diagnosis of erectile dysfunction.

After an average of 5 years, those who got prescriptions for Viagra (sildenafil) or similar drugs had an 18 percent lower risk of newly diagnosed Alzheimer’s disease than those who got none. The risk was roughly 40 percent lower in those who got more than 20 prescriptions during the 5 years.

However, those lower risks disappeared when researchers excluded men who were diagnosed with Alzheimer’s within the first 3 years. Since Alzheimer’s often starts years before it’s diagnosed, something else about the men who already had the disease could have made them less likely to get a prescription. As one of the study’s authors told Fortune.com, “an association does not mean a causal effect.”

What to do

This study doesn’t provide good evidence that drugs like Viagra can help prevent Alzheimer’s.