Antidepressants, among the top prescribed drugs on the planet, may be contributing to Alzheimer’s and other brain-destroying dementias, new Canadian research suggests.
According to the study, popular Prozac-like pills known as SSRIs — selective serotonin reuptake inhibitors — and other antidepressants are associated with a twofold increase in the odds of developing some form of dementia, including Alzheimer’s.
The association was even stronger for people who took antidepressants before age 65.
The study doesn’t prove cause and effect. However, the findings, which are published in the journal Depression and Anxiety, are expected to raise fresh concerns about a class of drugs experts say are being wildly and indiscriminately prescribed for everything from ordinary cases of “sadness” to insomnia, pain and hot flashes.
“They’re being prescribed ‘off label,’ meaning for non-depression related situations. They’re being prescribed to very young children and to the very old,” said Dr. Darrell Mousseau, a professor in the department of psychiatry at the University of Saskatchewan and the study’s senior author.
“They’re almost becoming the antibiotic of this century: ‘If you’ve got a disease, take an SSRI. It’s going to help you in one way, shape or form.’”
Mousseau doesn’t want to scare people off antidepressants. “They certainly do benefit some people,” he said. “But we do find this association (with dementia) and, if nothing else, I think the discussion needs to begin.”
Canadians are among the top users of antidepressants in the world. More than 50 million prescriptions were dispensed in 2015 alone, according to market research firm IMS Brogan.
Meanwhile, as people live longer the ranks of those with Alzheimer’s and other diseases of the brain grows. Globally, 47.5 million people have dementia; in Canada, the figure is 750,000 and is projected to double within 15 years.
Given the economic and social costs, scientists are searching for risks factors, and over the years there have been hints depression may be one, Mousseau said. “Still, not everyone who has depression gets Alzheimer’s disease, and not everyone who has Alzheimer’s has had depression.”
He wondered whether it is the depression itself, or the drugs used to treat it.
Mousseau has been particularly interested in a class of molecules called monoamines, which include the neurotransmitters serotonin and noradrenaline — brain messengers believed to be involved in depression.
The cells that make serotonin and noradrenaline are also among the first clusters of cells to die off in the brain changes leading to Alzheimer’s, he said.
“All of these anti-depressants act on these monamines,” added Mousseau, who holds a research chair in Alzheimer’s and related dementia jointly funded by the Alzheimer’s Society of Saskatchewan and the Saskatchewan Health Research Foundation. “It was just a logical step to look into what these drugs might be doing.”
His team searched the medical literature for relevant studies. In the end, only five from an initial pool of more than 4,000 met their criteria.
A total of nearly 1.5 million people were pooled from the five studies. Overall, the pooled estimates showed that people with dementia were twice as likely to have been exposed to an antidepressant compared with people without dementia.
When the studies involved people under 65, the risk was threefold, perhaps reflecting longer drug use, Mousseau said.
The link was strongest with the SSRIs, and lowest with older antidepressants.
The researchers couldn’t tell from the data set whether dose, or duration, meaning how long the person had taken an antidepressant, made a difference. And the analysis, in the end, included just five studies.
“But there is something to this association, even if it is not clear what it means,” said Dr. Joel Paris, past chair of psychiatry at Montreal’s McGill University.
Another study published last year from researchers in Taiwan also linked SSRIs with an increased risk of dementia.
However, a U.S. team reported two years ago the SSRI citalopram (sold under the brand name Celexa) appeared to reduce production of the deadly brain plaques tied to Alzheimer’s.
Paris said “replicability” — where one study should produce the same results of another if repeated exactly — “is a crisis in medical research. My own benchmark is to wait until there is enough for a (larger) meta-analysis.”
It’s possible any increased risk of dementia could be due to how much of an antidepressant the person was on, or from a bigger brain change that caused the more severe depression in the first place, the researchers acknowledged.
Still, they believe a link between antidepressants and Alzheimer’s is “biologically plausible.”
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Antidepressants May Be Doubling Risk of Alzheimer’s And Other Dementias, Study Suggests
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