Why links between antidepressants and dementia should be treated with caution

Anyone who takes antidepressants could be forgiven for feeling as though the negative publicity around them is never ending.

The latest concerning claim is that when people with dementia take an antidepressant, it may cause their memory problems and confusion to worsen faster than otherwise.

There is some basis to the headlines, but in reality, the findings are not as alarming as they may seem.

Use of antidepressants has been steadily rising for decades in most western countries, since the arrival of the Prozac class of medicines known as selective serotonin reuptake inhibitors, or SSRIs.

They are used for several mental health conditions, including anxiety and obsessive compulsive disorder as well as depression. In the UK about one in six adults are taking the medicines, leading to claims they are being overused.

The new concerns around dementia stem from an ongoing research project in Sweden, designed to discover if any medicines prescribed for other diseases have a protective effect against dementia.

It uses a registry of everyone in Sweden given a diagnosis of dementia from 2007 onwards, and records which medications they are taking and how their cognitive abilities have changed over time.

Two years ago the project found that people taking the cholesterol-lowering medicines statins have a lower risk of dementia, suggesting they should be investigated as potential dementia-preventing medicines.

In the latest study, published in BMC Medicine, the researchers investigated how dementia was connected with antidepressant use, analysing the records of nearly 19,000 dementia patients, tracked for about a decade.

They found that the cognitive abilities of those taking an antidepressant worsened slightly faster than those of people who weren’t on any such medication.

This could be because some SSRI antidepressants may block the actions of a brain signalling molecule called acetylcholine, said Dr Sara Garcia-Ptacek, a neurologist at the Karolinska Institute in Stockholm, who led the research.

Acetylcholine passes messages between brain cells, and some treatments for Alzheimer’s disease, a form of dementia, slightly improve memory by boosting acetylcholine levels.

But the finding should not necessarily alarm people who use antidepressants. For one thing, the study did not prove that the medicines were directly causing the faster memory decline. It could be that people who had worse dementia to begin with were more likely to be given antidepressants.

That’s because symptoms seen in the early stages of dementia can be confused with depression or anxiety. “Dementia can cause a kind of restlessness that can be interpreted as anxiety,” said Dr Garcia-Ptacek. “Symptoms such as apathy that show up in some types of dementia can be mistaken for depression.”

It could even be that the depression itself was causing people’s cognitive abilities to decline faster, rather than the drugs used to treat it, said Dr Richard Oakley at the Alzheimer’s Society.

“Because of these limitations, the study’s findings should be interpreted with caution and ideally replicated using other data sources,” said Dr Prasad Nishtala, a pharmacologist at the University of Bath, who was not involved with the research.

Even if the study has found a genuine side-effect from antidepressants, it seems to be a small one that would probably go unnoticed by patients and their families.

People’s cognitive abilities were measured using a test that gives a score from 0 to 30, where people without dementia usually have a result over 26.

People with dementia typically decline by about 3.3 points per year, although it is highly variable. Those taking antidepressants seemed to decline by about 0.5 points per year faster. “[This] may not be meaningful in everyday clinical practice,” said Dr Nishtala.

That kind of small effect size means that even if it is confirmed by further research, the downside would need to be weighed up against the positives from treating depression or anxiety.

“Depression itself is one of the worst things for bad cognition that you can possibly have. It causes problems with attention, it causes problems with initiative, it causes all kinds of memory issues,” said Dr Garcia-Ptacek. “A lot of people will see their cognition improve if they treat those things.”

So the new results are not necessarily a reason for peole to stop taking antidepressants, said Dr Garcia-Ptacek. She recommended that anyone concerned should discuss the findings with their doctor.