Certain medications used to treat heartburn and excess stomach acid appear to be linked to an increased risk of cognitive impairment in the elderly, a new study suggests.

Those medications are histamine-2 receptor antagonists, or H2As, marketed under names such as Zantac and Pepcid, according to the study by doctors at Indiana University. Nearly 1,600 blacks aged 65 and older participated in the study. Approximately 18% showed signs of diminished cognitive capacity during follow-up, the report indicates.

Previous studies also have pointed to adverse effects of the drugs, according to the study report in the Journal of the American Geriatric Society.