Figure 6.Melatonin can phase shift and, in some cases, synchronise circadian rhythms in some sighted and blind subjects with suitable timing of treatment and dose. Shown are the times of the calculated peaks (acrophases) of urinary 6-sulphatoxymelatonin (squares) and cortisol (circles) of a free-running blind subject with a period of 24.57h treated with placebo or 5mg melatonin daily, timed to phase advance the internal clock. Note that with melatonin a 24h period is maintained (with beneficial effects on sleep). Redrawn from reference (147).