If I prescribe an antidepressant, patients always ask, “How soon will it work?”

The standard answer, one that’s been in the literature for years, is “two weeks,” with the caveat that full effects may take weeks longer.

But clinicians have always suspected that some changes come about earlier. A (reasonably unreliable) rule of thumb is that a good, even if transient, initial response predicts a solid outcome later. And there have always been studies showing some improvement within days, so that patients are “better but not well.”

Now out of England comes research that should enter Guinness World Records.

Dr. Philip Cowen, a serotonin expert and head of the Psychopharmacology Research Unit of the Department of Psychiatry at Oxford, reports changes shortly after administering a single pill. When he gave an antidepressant to depressed patients, after four hours they were better able to pick out happy faces from a collection of images and to recall positive words from a list. Patients given a placebo showed no such change. The press release, from the Royal College of Psychiatrists, is titled "Antidepressants ‘can change the way depressed people see the world in just four hours.'" It's worth reading — won’t take you a minute.