Do prescription drugs cause dementia?

All drugs have side effects, and taking a prescription drug always means weighing the benefits against the risks. Many prescription drugs also carry long-term risks – effects that won’t be apparent after taking a medicine briefly but could happen years later if the drug is taken over a long time.

Many people are worried about developing dementia – and as the UK population ages, this worry is increasing. One in 14 people over the age of 65 are living with dementia, and 57% of people in this age range say they fear dementia more than any other condition. It’s understandable, then, that people want to be informed about the risks of the medications they’re taking and understand how they might increase their risk of developing dementia.

What is dementia?

Dementia is an umbrella term for a group of diseases that affect cognition. There are over 200 subtypes of the condition. Alzheimer’s is the most common form of dementia, making up about 60% of the diagnoses in the UK. Age is the biggest risk factor for dementia, but lifestyle factors and genetics also play a role. Dementia has a common set of symptoms, but each subtype presents differently – and it is possible to have more than one kind (mixed dementia).

Can certain medications cause dementia?

It’s reductive to say prescription drugs ’cause’ dementia – we can only say that certain drugs are correlated with an increased risk of developing it. The science behind cause and effect can be murky and complex. Statins are a good example of this.

Some people have been reluctant to take statins, drugs that help to lower cholesterol, because they have heard they cause dementia. This arose from early case reports about adverse effects on cognitive function, particularly in older patients. However, this was in a limited number of cases and the impaired cognitive function was only short-term. Follow-up studies found that statins were actually associated with a 20% decrease in the risk of developing dementia.

So, does this mean that taking statins protects you from developing dementia? Not quite. Studies testing whether taking statins directly reduced dementia risk or helped to improve memory found no effect. It’s more likely that the benefits to the heart and circulatory system gained from taking statins are responsible for this risk reduction – but we still don’t fully understand the actual reasons. Lack of exercise and smoking are associated with high cholesterol – and both of these also increase dementia risk. It’s a complex picture, and it’s often hard to test a drug to see if it directly causes something else due to other factors, like weight and lifestyle. These factors are called confounding variables.

Another confounding variable is that many of the drugs that have been linked to dementia are commonly prescribed to older patients – who already are at higher risk of developing dementia.

With this in mind, let’s take a look at some of the types of drugs that are associated with an increased risk of developing dementia.

Anticholinergic drugs

Out of all of the drugs associated with an increased risk of dementia, anticholinergics have the strongest link.

Acetylcholine is an important neurotransmitter that plays a role in movement, memory, learning and attention. Low acetylcholine levels are associated with Alzheimer’s disease. Anticholinergics block the function of acetylcholine.

There isn’t just one type of anticholinergic drug. They’re used to treat many conditions – incontinence, Parkinsons, respiratory conditions and heart disease. Some drugs have anticholinergic effects that aren’t directly related to the condition they’re treating – certain antidepressants, antipsychotics and antihistamines inhibit acetylcholine.

A study in The Journal of the American Medical Association found that high use of these drugs was associated with an increased risk of dementia. First-generation antihistamines were one of the drug classes the study reported as being used the most – these are anti-allergy drugs that have mostly been replaced with newer antihistamines because they cause sleepiness. However, some of these drugs can still be bought over the counter as sleep aids – like diphenhydramine, the active ingredient in Nytol.

Benzodiazepines

The evidence linking benzodiazepines to dementia is mixed. Some studies have found links, but others haven’t.

A study in The British Medical Journal took a large group of people who had been diagnosed with Alzheimer’s and matched them with a group of people who hadn’t and looked at whether people in these groups had been prescribed benzodiazepines. They found that past benzodiazepine use was associated with an increased risk of Alzheimer’s, and long-term use made this association stronger, which suggests a direct association between the two.

However, The Alzheimer’s Association repeated this study with the knowledge that anxiety, agitation and insomnia – all things that benzodiazepines are prescribed for – are also early symptoms of dementia. This is a confounding variable, so they excluded people who were taking benzodiazepines for these reasons from their sample and focused on people who were prescribed them for unrelated conditions, like chronic back pain and sciatica. They did find a link between benzodiazepine usage and risk of dementia – but it was too low to be statistically significant.

Prescription drug addiction to benzodiazepines is unfortunately very common, particularly in elderly patients – people aged between 65 and 80 are prescribed benzodiazepines at a higher rate than any other age group. Even if the evidence linking them to dementia is mixed, long-term use of benzodiazepines is risky.

Benzodiazepines should not be taken for longer than two weeks. Taking them for longer than this increases the risk of prescription drug addiction side effects, and these effects are especially pronounced in elderly patients.

Heartburn and acid reflux medications

These drugs reduce stomach acid and come under two classes – proton pump inhibitors, like omeprazole, and H2 receptor antagonists, like cimetidine. Proton pump inhibitors usually work better and are prescribed first, but if they don’t work for you, you may be prescribed an H2 receptor antagonist instead.

Both classes of drugs have been associated with an increased risk of dementia in some studies, but others have not found a link. If this link does exist, some studies have proposed that it could be because some of these drugs have anticholinergic potential. They’re also associated with B12 deficiency, which is also linked to cognitive decline.

Weighing the risks

Taking any medication always involves weighing the potential risks and benefits of taking a drug and the risks of not taking it. For some conditions, the ramifications of leaving the condition untreated outweigh the risks of taking it.

If you or someone you care for are taking a medication that you have concerns about, discuss your concerns with a doctor. There may be alternative medications associated with lower risk that you can switch to.

Older people, who are at most risk of developing dementia, are often prescribed multiple drugs for multiple conditions. This means regular medication reviews should be undertaken to minimise harmful drug interactions and ensure medication that is no longer benefiting them can be stopped.

Prescription drug addiction treatment may be necessary if a person has been prescribed some medications, such as benzodiazepines, for longer than is appropriate. If this is the case, reach out to us – we can help.