TORONTO -- Cognitive enhancers -- drugs given to Alzheimer's patients to improve concentration, memory, alertness and moods -- do not improve mental function in people with mild cognitive impairment, researchers say.

Mild cognitive impairment, or MCI, is marked by memory lapses and problems with language, thinking and decision-making that go beyond what's expected with normal aging, but are not as pronounced as the changes that would signal the decline of dementia.

However, up to 17 per cent of MCI patients do go on in time to develop a dementia such as Alzheimer's disease.

Doctors sometimes prescribe cognitive enhancers to people with mild cognitive impairment in the hope of helping improve their memory and day-to-day functioning. In Canada, physicians need special authorization to give the medications to people with MCI.

"More and more patients and their families are requesting these medications," said Andrea Tricco, a scientist at St. Michael's Hospital in Toronto, who led a study looking at the drugs' effects on MCI patients.

"It is a form of medication creep in that a lot of people seem to be going to their doctors and asking for them."

In a review of international studies that tested cognitive enhancers in people diagnosed with mild cognitive impairment, the Toronto researchers found the drugs had no benefit over the long term and had numerous side-effects.

The study, published Monday in the Canadian Medical Association Journal, assessed the results of eight clinical trials that involved almost 5,000 MCI patients, aged 66 to 73. Patients were given one of four cognitive enhancers -- donepezil, rivastigmine, galantamine and memantine -- or a dummy pill.

"We found that they weren't helpful and that actually they also caused harm," said Tricco. "So they caused significantly more headaches, nausea, vomiting and diarrhea, compared to patients who received placebo."

"Patients and their families should consider this information when requesting these medications," the authors write. "Similarly, health-care decision makers may not wish to approve the use of these medications for mild cognitive impairment, because these drugs might not be effective and are likely associated with harm."

Dr. Serge Gauthier, director of the Alzheimer's disease research unit at McGill University's Centre for Studies in Aging, said the authors' conclusions are in line with recommendations of the 2012 Canadian Consensus Conference on the Diagnosis and Treatment of Dementia.

"We reiterated that this is the wrong stage (of dementia) to treat," said Gauthier, noting that there are no medications at this point to slow the process of mild cognitive impairment.

"Frankly, the kind of drug you need is often an antidepressant more than an Alzheimer's-specific drug because (patients) realize there's a change in their cognitive ability," he said Monday from Montreal. "They worry it's going to get worse, and if you need a pill it's often an antidepressant or something for anxiety."

However, eventual dementia isn't a given for all people with mild cognitive impairment; some never get worse, and a few eventually get better, depending on the underlying cause.

Doctors now are able to predict with greater accuracy which MCI patients will go on to develop a full-fledged dementia, using brain scans and tests looking for specific proteins in spinal fluid, said Gauthier.

That has changed how doctors classify patients within the spectrum of mild cognitive impairment and how they should be treated.