People who are repeatedly diagnosed with depression are at an increased risk of developing Alzheimer's disease (AD) in later life. Researchers found that depressive symptoms up the risk of AD because antidepressants are often initiated in people with the condition before the diagnoses.

Researchers from the University of Eastern Finland wanted to investigate the incidence of antidepressant use in people with and without AD. They found that among those with AD, the start of using antidepressants was most common six months after the diagnosis and more frequently than those who have no AD, even after four years after the diagnosis.

"The incidence of antidepressant use was higher in persons with AD than in comparison persons, and it was not explained by history of hospital-treated psychiatric disorders," said the researchers.

The findings, published in the International Journal of Geriatric Psychiatry, involved more than 62,000 people from Finland with AD diagnosed from 2005 to 2011, and was based from data analysis from the Medication use and Alzheimer's disease group. The researchers matched them with counterparts without AD.

They included the number of antidepressants dispensed from 1995 to 2012. They allotted a one-year washout period wherein the rate of new antidepressant users was measured every 6-month period starting from nine years before and four years after AD diagnoses.

The team found that the start of antidepressant use among those with AD in later life, was more common nine years before the diagnoses than the ones without diagnoses of the most common type of dementia. Overall, the incidence of antidepressant use in AD patients was markedly higher compared with those people without the disease.

Though the finding is surprising, the result may be linked to more frequent use of antidepressants for depressive symptoms since depression has been linked to increased AD risk in the past.

After 13 years, about 42 percent of AD patients and 22 percent of those without AD initiated antidepressant use. Selective serotonin reuptake inhibitor (SSRI) drugs are the most common type of antidepressants used, the study found.

"Widespread use of antidepressants in persons with AD is concerning as their efficacy is controversial and their use is associated with adverse events," the researchers concluded.

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