I also saw this and was curious. It could just be an uncontrolled third correlate, like the severity of insomnia mentioned in other comments, or something else. But I think there are plausible causal mechanisms.
One relevant thing is that the doses they were prescribed were almost certainly far too high.
I think you could make an argument for anything up to 1 mg. Anything beyond that and you’re definitely too high. Excess melatonin isn’t grossly dangerous, but tends to produce tolerance and might mess up your chronobiology in other ways.
So my guess is that the prescribed dose is even higher than the 5-30x too high that’s the standard non-prescription dose. Even with the fast half-life, that melatonin is telling those patients minds and bodies (several metabolic processes I assume) that they should be sound asleep when they shouldn’t. High doses will probably also cause tolerance, as all of the brain is an adaptive system with tons of negative feedback loops that cause tolerance at many scales (citation: me), and I weakly gather that the rest of the body works the same way. The combination of sleep signals out of place and strong tolerance could wreak havoc in a variety of ways.
I suspect the other correlation might be that doctors who ignore all of this and prescribe high-dose melatonin for sleep disorders are bad doctors. But that’s speculation, aside from the above hypothesis.
Alexander continues:
Based on anecdotal reports and the implausibility of becoming tolerant to a natural hormone at the dose you naturally have it, I would guess sufficiently low doses are safe and effective long term, but this is just a guess, and most guidelines are cautious in saying anything after three months or so.
So I continue to take .5mg melatonin nightly as a way to gain voluntary control over my sleep schedule.
There’s also some evidence that the body may not produce melatonin properly if we’re in bright artificial light up to bedtime. So the supplementation I’m doing might actually be doing something that the body would do in its natural environment but doesn’t do now. This evidence was cited by a trustworthy but non-rationalist person and I haven’t tracked it down myself, so I don’t know how likely this really is to be true.
The rest of that essay on melatonin also seems highly useful.
I also saw this and was curious. It could just be an uncontrolled third correlate, like the severity of insomnia mentioned in other comments, or something else. But I think there are plausible causal mechanisms.
One relevant thing is that the doses they were prescribed were almost certainly far too high.
Scott Alexander claims and argues convincingly that the evidence for this is clear and overwhelming in his essay Melatonin: Much More Than You Wanted To Know
So my guess is that the prescribed dose is even higher than the 5-30x too high that’s the standard non-prescription dose. Even with the fast half-life, that melatonin is telling those patients minds and bodies (several metabolic processes I assume) that they should be sound asleep when they shouldn’t. High doses will probably also cause tolerance, as all of the brain is an adaptive system with tons of negative feedback loops that cause tolerance at many scales (citation: me), and I weakly gather that the rest of the body works the same way. The combination of sleep signals out of place and strong tolerance could wreak havoc in a variety of ways.
I suspect the other correlation might be that doctors who ignore all of this and prescribe high-dose melatonin for sleep disorders are bad doctors. But that’s speculation, aside from the above hypothesis.
Alexander continues:
So I continue to take .5mg melatonin nightly as a way to gain voluntary control over my sleep schedule.
There’s also some evidence that the body may not produce melatonin properly if we’re in bright artificial light up to bedtime. So the supplementation I’m doing might actually be doing something that the body would do in its natural environment but doesn’t do now. This evidence was cited by a trustworthy but non-rationalist person and I haven’t tracked it down myself, so I don’t know how likely this really is to be true.
The rest of that essay on melatonin also seems highly useful.