May 9, 2016 -- Could your chances of getting dementia depend on what’s in your medicine cabinet?
The drugs involved in the study are known as anticholinergics. They work by blocking a brain chemical called acetylcholine, which is crucial for memory. Although this isn’t the first time researchers have looked at this link, the new study looked at about 100 over-the-counter and prescription drugs that work in this way, ranging from the antidepressant Paxil (paroxetine) to the allergy drug Benadryl (diphenhydramine) to the motion sickness remedy Dramamine (dimenhydrinate).
The experts found a strong link between the drugs and dementia, but they didn't prove the meds directly cause it. WebMD asked the lead researcher on the recent study and an expert on Alzheimer's disease to help people taking the drugs understand what to know and do.
What did this study actually show regarding these drugs and dementia?
The brains of those people taking the medicine did not work as well as the brains of those not taking them. "We saw an increased risk of getting dementia over time," says researcher Shannon Risacher, PhD, assistant professor of radiology and imaging sciences at the Indiana University School of Medicine.
Older adults who took the drugs had poorer thinking skills than those not taking them, she says. Their brains were also smaller, especially in the areas important for memory and other thinking skills.
The researchers looked at the brains of 451 men and women, with 60 taking one or more of the anticholinergics medicines. Their average age was 73, and they had normal thinking skills and brain volume.
Study participants took the medicines on average for about 7 years.
Overall, the researchers found that those on the medicines were ''four times more likely to develop either mild cognitive impairment [which often develops into dementia] or dementia'' than those not taking the medicines. The brain problems developed over a time frame ranging from 6 months to about 8 years, Risacher says.
The findings echo previous research, says James Hendrix, PhD, director of the global science initiatives at the Alzheimer's Association. "It's one of those things we have known for a while,'' he says.
Are some of the drugs more likely to increase the risk of dementia than others?
Yes. The researchers classified the drugs into three groups, from those with the lowest anti-cholinergic properties to the highest. "What we really looked at were the [drugs scored as] 2's and 3's, with medium and high anticholinergic properties," Risacher says. Those scored as 1 were also linked with a higher risk of dementia, but not as strongly, she says. She plans to study this class further. Among drugs in this class are anti-anxiety drugs Valium (diazepam) and Xanax (alprazolam), the heartburn drug Tagamet (cimetidine), and the allergy drug Claritin (loratadine).
A list of drugs in groups 1, 2 and 3 (not all on this list were taken by the study participants) is here.
How do the drugs affect the brain and how do they boost dementia risk?
"They reduce the activity of, or block, acetylcholine," Risacher says. "It is very important for memory."
While some drugs used to treat Alzheimer's work by increasing the amount of acetylcholine to improve memory, she says, "these drugs essentially do the opposite."
You found only a correlation or association, correct?
Yes, but ''it's a pretty strong association," Risacher says. While the research cannot prove cause and effect, she says the link held even after the researchers took into account other things that might affect how the brain works, such as other medical conditions or a history of brain injury.
Hendrix agrees the link is strong. But as with all studies that show an association, there could be other things explaining the results, he says.
What is the absolute risk to a single person?
That's impossible to calculate, Risacher says. "People metabolize these drugs at different rates, and they could have different effects on different people," she says. But the researchers did find that the risk increased even more in those people on multiple anticholinergics.
Should people stop taking these medicines?
The Consumer Healthcare Products Association (CHPA), an industry group representing makers of over-the-counter products, issued a statement, pointing out that the study sample was relatively small, with 60 people regularly taking the drugs.
"It is important to remember that the active ingredients are approved by the U.S. Food and Drug Administration (FDA) and recognized as safe and effective when taken as instructed on the product label," it says.
CHPA also stressed that no cause and effect has been proven, only a statistical association, and that everyone agrees more research is needed.
Hendrix and Risacher agree a first step is to have a talk with your doctor.
Consider how long you're using the drugs, Hendrix says. "If you are taking it for a week, I wouldn't think that's a huge risk. If you are taking it for 3 years, that would be more concerning to me."
Some of the meds have alternatives that may treat your condition, Risacher says. Talk with your doctor about whether the benefits of a certain drug outweigh the risks, she says.
The average age in your study was 73. Can you say if the findings also apply to younger people?
It's hard to know, Risacher says. "What I can say is, older adults are probably more sensitive to the effects of all these drugs. But the studies haven't been done. And acetylcholine naturally declines with age."
If you quit the drug, does the risk disappear?
"We didn't look at that," Risacher says. Although some studies have suggested that stopping the medicines may lower the risk, another found the damage couldn't be reversed.