Emily Hong & Meg Seymour, PhD
You may have heard the media coverage that common medications may increase the risk for dementia. These medications include a variety of drugs, including antihistamines (like Benadryl), some antidepressants, and drugs that help people with Parkinson’s.1 What do these drugs all have in common, what do you need to know about them, and are there really risks to taking them?
The drugs in question are called anticholinergic medications. They block the action of a neurotransmitter called acetylcholine. Acetylcholine is important for memory, attention, and learning. Because of this connection to memory and the brain, the side effects of some anticholinergic drugs can include dementia-like symptoms, such as memory loss and confusion.
In most cases, these side effects go away after people stop taking the medications.2 However, people taking some anticholinergic drugs may have an increased risk of developing dementia later.2, 3, 4 It is important to note that there are many types of anticholinergic drugs that treat many conditions. The risk may be specific to some drugs. So, it’s important to assess each type of anticholinergic drug separately.
A 2019 study conducted in England included 284,343 patients.4 It looked at 56 different anticholinergic drugs to see their effects on risk for dementia. The study found that people had a higher risk for dementia if they took:
- Antiparkinson drugs,
- Antimuscarinics (Used to treat an overactive bladder), and
- Antiepileptic drugs.
The study also found that the below-listed drugs did not increase the risk of developing dementia:
- Antihistamines (Used to treat allergy symptoms),
- Gastrointestinal antispasmodics (Used to prevent spasms of the stomach, bladder and intestines),
- Skeletal Muscle Relaxants (Used to relax and reduce tension in muscles, such as muscle spasms or hyperreflexia),
- Antimuscarinic bronchodilators (Used to relax the muscles in the lungs, allowing breathing to come easier), and
- Antiarrhythmics (Used to treat heart rhythm disorders).
Another 2019 study looked at 367,871 patients living in Korea, but focused on a much narrower question. This study only looked at whether anticholinergics increased the risk for developing Alzheimer’s disease, which is a specific type of dementia.5 The study found that taking antihistamines and antimuscarinics increased risk for developing this specific type of dementia. However, the risk was not as high for antihistamines than for other anticholinergics, such as antidepressants.
In looking at the results of these two huge studies, it is important to keep in mind the differences in how they were conducted:
- The English study looked at all types of dementia, but the Korean study only looked at a specific type of dementia called Alzheimer’s.
- The Korean study found a higher risk for adults who started to take the drugs at ages 60-64 compared to adults who started taking them when they were over 65. The British study did not distinguish between patients who started taking the drugs before or after the age of 65, and could not adequately study the impact of age because only 2% of the people in the British study were less than 65 years old.
- Because the studies were conducted in different countries, there may be differences in why and how the drugs were prescribed, and for what types of patients.
Even with those differences in mind, both studies show that the people most at risk for developing some type of dementia were those who were prescribed higher doses of certain anticholinergic drugs for many years. The studies followed participants for 10 years, and previous research following people for a shorter time did not find an increased risk of dementia.6 These two studies show that overall, people who use more of some types of anticholinergic drugs for many years are more likely to develop dementia.
Keep in mind that these are observational studies – studying what happens to people in the real world. That’s different from a clinical trial, where some people are assigned by researchers to take a particular medication and compared to patients who didn’t get that medication. We don’t know if the people who developed dementia differed from those who didn’t develop dementia in other ways besides their use of anticholinergics. For example, the drugs were prescribed to treat a particular condition, but it is possible that something about the condition itself (not the medication used to treat it) may have increased the risk for dementia.
The studies have some further limitations as well. For example, the studies only included men and women who were 55 years and older because dementia is rare at younger ages. This means that the study results could have been different if the study included long-term use as a younger adult. The studies also did not include information about whether patients had a family history of dementia. Also, the studies measured the medications that were prescribed to the patients, but there is no way to know if the patients took the medications as they were prescribed. Participants may have also taken anticholinergic medications that are available over-the-counter, such as allergy medication or sleep aids.
All medications have some risks, so it’s important to consider whether the benefits outweigh the risks for you. If you are concerned that the medication you are taking or have been prescribed could be linked to an increased chance of developing dementia or dementia-like symptoms, consider whether this is a risk you want to take, or whether you want to consider not taking some of these anticholinergic medications in the future. You may want to discuss these studies with your doctor.
- Merz, Beverly. “Common Anticholinergic Drugs like Benadryl Linked to Increased Dementia Risk.” Harvard Health Blog, 23 Oct. 2019, https://www.health.harvard.edu/blog/common-anticholinergic-drugs-like-benadryl-linked-increased-dementia-risk-201501287667.
- Gray, S. L., Anderson, M. L., Dublin, S., Hanlon, J. T., Hubbard, R., Walker, R., … & Larson, E. B. (2015). Cumulative use of strong anticholinergics and incident dementia: a prospective cohort study. JAMA Internal Medicine, 175(3), 401-407. https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2091745
- Fox, C., Smith, T., Maidment, I., Chan, W. Y., Bua, N., Myint, P. K., … & Campbell, N. (2014). Effect of medications with anti-cholinergic properties on cognitive function, delirium, physical function and mortality: a systematic review. Age and Ageing, 43(5), 604-615. https://academic.oup.com/ageing/article/43/5/604/2812269
- Coupland, C. A., Hill, T., Dening, T., Morriss, R., Moore, M., & Hippisley-Cox, J. (2019). Anticholinergic drug exposure and the risk of dementia: a nested case-control study. JAMA Internal Medicine, 179(8), 1084-1093. https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2736353
- Joung, K. I., Kim, S., Cho, Y. H., & Cho, S. I. (2019). Association of Anticholinergic Use with Incidence of Alzheimer’s Disease: population-based Cohort study. Scientific Reports, 9(1), 1-10. https://www.nature.com/articles/s41598-019-43066-0#Sec10
- Campbell, N. L., Boustani, M. A., Lane, K. A., Gao, S., Hendrie, H., Khan, B. A., … & Hall, K. (2010). Use of anticholinergics and the risk of cognitive impairment in an African American population. Neurology, 75(2), 152-159. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2905930/