Antidepressants begin casting more 'positive light' in just 4 hours

A single antidepressant tablet makes a depressed person see the world in a more positive light just four hours after swallowing it, a new study has shown.

Dr Philip Cowen, professor of pharmacology at the Department of Psychiatry at the University of Oxford, told delegates at the Royal College of Psychiatrists' Annual Meeting in London that antidepressant medication starts to work far faster than most clinicians assume.

"Depressed people interpret the world in a negative way," he said. "They become stuck in this state. Negativity causes depression and depression causes negativity and, whatever happens, events will be interpreted in a negative way."

Antidepressants elevate mood, which in turn leads to a depressed person becoming more positive and interpreting things that happen to them in a positive way. Prof Cowen said: "Antidepressants change biases. People who take them begin to see the world in a positive light," said Prof Cowen.

But it does not take weeks for this change to happen. Prof Cowen and his colleagues gave 30 depressed people one single 4mg dose of reboxetine (Edronax^®, Vestra^®) - which inhibits the update of both serotonin and noradrenaline in the brain - and compared them with 30 'controls' who were given a placebo.

The researchers asked both groups to carry out a series of simple tasks, including picking out the 'happy' facial expression from a line of faces, and recalling positive rather than negative words. They found that the placebo group were poor at spotting happy faces. They also tended to remember the negative words and were slow to categorise positive information.

However, four hours after taking a single dose of reboxetine, the drug group were as capable of remembering the positive words and spotting the happy expression as people who were not depressed.

Prof Cowen said: "People with depression interpret their internal and external worlds in a negative way. The current antidepressant drugs take away the automatic feelings of negativity at the first dose."

Antidepressants affect mood indirectly by abolishing the negative bias in the way that depressed people appraise personal and social experience at a subconscious level.

While there might be little change in overall conscious mood, Prof Cowen concluded: "Over time, and with a fair wind, this can lead to feeling better and improve the changes of recovery."

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Cowen P. How antidepressant drugs challenge depressive realism. RCPsych Annual Meeting, London 2008 Jul 3.