A reader asks:

 In the question on “the mechanism of action of the agitation side effect,” one of your suggestions was to try light later in the morning. Could you explain more about this? It was the one suggestion that is not immediately obvious, if the point is to reduce exposure a bit.


To understand this suggestion, you need to learn a bit about the physiology of the internal circadian clock. The clock is maximally sensitive to light input — on average — during the last 90 minutes of habitual sleep (i.e., sleep without artificial early waking). This is the time interval during which you can most easily reset your clock earlier, and such resetting is integral to the antidepressant effect. After habitual waking, the clock gradually loses sensitivity over the next 3-4 hours. Thus, by using the light later in the morning, you can effectively reduce the treatment dose. (Alternatively, you can get a similar effect by using less light earlier in the morning.)