— Antidepressant drugs can improve people's sense of taste, a new study has revealed.
The surprising findings could lead to a new taste test that predicts how a person will respond to various antidepressants, the researchers say. The findings may also help explain why patients taking such medication often gain weight.
Lucy Donaldson at the University of Bristol, UK, and colleagues tested the taste bud acuity of 20 healthy volunteers. Donaldson took cotton swabs that had been dipped in bitter, sweet or sour solutions of varying concentrations and dabbed these swabs on subjects' tongues to determine their normal taste sensitivity.
Each participant then received either a placebo pill or one of two types of common antidepressants paroxetine or reboxetine. Researchers re-tested volunteers' taste sensitivity two hours after giving them the pills.
Whereas the placebo caused no change in participants' ability to taste, both types of antidepressants increased their sensitivity to bitter tastes.
In addition, the team discovered that participants were more sensitive to sweet flavours if they took an antidepressant tablet that increases levels of the brain chemical serotonin (paroxetine); and more sensitive to sour flavours if the pill they took acts by increasing the levels of brain chemical noradrenalin (reboxetine).
Those on paroxetine picked up on sweet tastes at 27% lower concentrations than before treatment. Previous studies have shown that serotonin helps sweet taste receptor cells transmit signals, Donaldson says.
Reboxetine allowed participants to detect sour tastes at 22% lower concentrations than before treatment. Noradrenalin could help sour taste receptor cells on the tongue send signals, Donaldson speculates.
There have been some preliminary reports that depressed patients have a diminished ability to taste, says team member Jan Melichar, also at the University of Bristol. He believes that the brain stem, which produces and distributes serotonin and noradrenalin to other parts of the brain and the tongue, produces less of these neurotransmitters in depressed people.
Researchers plan future tests to discover whether such patients have unusually low sensitivity to sweet and sour tastes. If some depressed people do have a dulled sense of either sweet or sour taste, this could indicate the nature of any neurotransmitter deficiency they might be suffering from.
And a simple taste test in the doctor's office might one day suggest whether a drug that affects serotonin levels or one that affects noradrenalin would work best for a given patient.
Hit and miss
At present, the prescribing of drugs for mental illness can be a case of trial and error. About 60% to 80% of the time, the first antidepressant prescribed to a patient will work, according to researchers. But for those patients who do not respond to the drugs, the disappointment can contribute to their depression. "The more weeks and months that pass, the more stuck they are," says Melichar.
Neuroscientist Bruce McEwen at Rockefeller University in New York, US, says a simple taste test would be a useful tool for diagnosis, especially if combined with genetic tests currently being explored to predict patients' response to antidepressants (see Genes reveal likely response to antidepressants). But he stresses that it must first be demonstrated that depressed individuals have significantly different taste sensitivity compared to healthy people.
The new findings might also shed light on why antidepressants have been linked to weight gain: "It's possibly because food tastes better" for patients taking such medication, says Donaldson.
Journal reference: Journal of Neuroscience (DOI:10.1523/jneurosci.3459-06.2006)