Chronotherapy is not a drug. It is a therapy where you are told to go to bed progressively later and later until on a "normal" schedule. It has recently been shown to cause N24 and while some sleep doctors have gotten the memo many still have not and are still recommending Chronotherapy.
Hi, you are correct that the term chronotherapy has been used to include adjusting sleep timing to treat delayed sleep onset.
Typically chronotherapy refers to any therapy in which circadian timing is important. In sleep issues this also includes melatonin, light therapy, and some drugs. There are a number of melatonin drug alternatives that have been tried.
When adjusting sleep timing used with sleep therapy I see it referred to as phase-delay chronotherapy. In other words, a specific kind of chronotherapy.
The risk of phase delay chronotherapy inducing non-24 seems to be rare. There are some anecdotal cases. The actual incidence appears to be hard to find, though statistics are available. See here:
http://www.nejm.org/doi/full/10.1056/NEJM199212103272417
In 1983, one of us
3 described a 28-year-old man with DSPS who underwent chronotherapy and found himself unable to stop his sleep period from rotating around the clock or restore his rhythm to a 24-hour schedule. Instead, hypernyctohemeral syndrome developed,
4 with a persisting 25-hour sleep–wake cycle. This rare syndrome is extremely debilitating in that it is incompatible with most social and professional obligations. Since then, we have diagnosed hypernyctohemeral syndrome in two men 22 and 28 years old, in whom it developed after chronotherapy for DSPS.
However this is an old reference.
This site discusses some of the issues:
http://www.circadiansleepdisorders.org/info/N24chrono.php
Some persons with DSPS do go on to develop Non-24 in the course of their lives, but this is very rare. The vast majority of people with DSPS never progress to Non-24.
Chronotherapy is not the only factor that can cause someone with DSPS to develop Non-24. Anecdotal reports suggest that this can also happen in some persons who have not done chronotherapy. However this is rare. The vast majority of persons with DSPS will never develop Non-24.
Doing chronotherapy however, changes the equation and seems to put persons with DSPS at significant risk of developing Non-24, even people who otherwise would have remained in a stable DSPS indefinitely.
However none of this research seems to be about ME or CFS. Given the brain involvement in ME its possible we are at higher risk. Its also possible we are at risk even without phase-delay chronotherapy.
I have seen a high proportion of phase-delay and non-24 in long term ME patients. We have a host of sleep issues. These problems I see, anecdotally of course, start appearing at about year 3 and being very common after year 10 of illness.
This is an area that could use far more study in ME. If we are hypometabolic that might be all that is needed to put us at risk, particularly if we have fluctuating daily temperatures.
I now live with a free running circadian pattern. This has immensely improved symptomology, while at the same time inducing the typical social problems found with non-24.
However at times this breaks down and its like my circadian rhythm is six hours, not 24 or 25, though I have only seen this in the last few years, and typically it resolves in a few days or weeks.
PS Another ME patient I have discussed this with has the same issue as me that sleep onset can advance, hold, or reverse by a highly variable time. Its not an hour. Its anything from minutes to eight hours. Its just commonly more like an hour.