Melatonin

That pairing is the peak of a curve drawn across many different trials, not a regimen any single trial actually ran. Nobody has yet put it head to head against the usual 30-minutes-before dose, which is the comparison that would settle it. The pooled trials span 1987 to 2020 and differ widely in whom they enrolled.

The trial registry lists two melatonin trials in heart failure, one withdrawn and one with no update since 2020. Of the registered melatonin insomnia trials screened, only 13% had posted results, so some safety data may never have been published.

The study measured an inherited tendency to insomnia and never looked at melatonin or any sleep aid. Everyone in it was of European ancestry. About 28% of the people in the insomnia gene data were also in the heart data, which can pull the estimate toward an ordinary association, though the authors judged that bias likely small.

This rests on one trial, and its benefit showed in sleep and tiredness ratings rather than an overall jet lag score. About a quarter of those enrolled were dropped for missing doses or leaving. In the largest jet lag trial, neither 0.5 mg nor 5 mg beat placebo.

The pooled scores come from four small trials of 17 to 52 people, published from 1987 to 1992. Two later trials that found no benefit, one of them the largest at 257 people, were left out of that pool. A re-analysis that counts them finds about half the effect of a pooling that leaves them out. Ratings varied so much between people that their spread often exceeded 90% of the average score, so the 40% is a gap between group averages, not what each traveller felt. Scores were compared after the flight, not as change from how each person felt before it.

The review mixed trials in children and adults, so the rates are not adults' alone. Only 8 of the 37 trials were rated good quality, and 13 were rated poor. No rate was given for palpitations.

Of the 90 reports, 19 had enough detail to judge whether melatonin caused the problem, and the dose taken was often unknown. Reports show what was noticed, not how often it happens. Limits on melatonin supplements differ by country, from 0.3 mg in Belgium and Germany to under 2 mg in France.

The three trials enrolled 201 people in all. The estimate ran from about a 2-point fall to a 6-point rise in ejection fraction, so a small effect either way is not ruled out. Harms were reported inconsistently across the trials. A second review reaching the same result drew on some of the same trials.

A ranking says which treatment the evidence supports better, not how much it helps. Of the five studies a 2014 review accepted, three tested sleeping pills and one tested light. Melatonin's rating rests on the fifth, an earlier review of ten trials, graded low quality because doses and schedules varied. A later reading of the head-to-head found melatonin alone did not clearly lower overall jet lag.

Pieces have been tried alone: non-drug fixes after real flights mostly failed, with 9 of 13 controlled studies finding no change in one review. Three days of earlier bedtimes with morning light moved the clock 1.5 to 2.1 hours in the laboratory, with no flight afterwards. Six mountain bikers combined all three before flying to Tokyo, with no comparison group.

Laboratory studies of melatonin and the body clock continued after 2004, without flights. Newer drugs that act on melatonin's receptors have had jet-lag trials of their own, which this count leaves out. The registry figure comes from the main US trial registry alone.

Benefit after westward flights rests on fewer trials: two in one pooling, four in another. Two trials found benefit after westward trips of twelve or more time zones.

The older pooling mixed adults and children without separating them, so its average may be describing the children in it. In the newer one, the adult comorbid group rests on a single study out of 24, and only four of those 24 covered insomnia alongside another condition at all. The two reviews draw on overlapping trials, so they are not independent checks on each other. Neither names which other conditions those four trials covered.

The open question is who melatonin's average benefit belongs to. Pooled across all ages it helped; split by age, adults whose insomnia arrives on its own showed nothing significant, and the benefit looks to belong to children.

The data allow anything from about 13 minutes faster to 3 minutes slower, so a modest gain is not ruled out. The review's headline figure pooled jet lag with shift work and sleep deprivation. Two single trials, the first among them, did report faster sleep onset on melatonin.

One review found melatonin did not speed falling asleep and called it unproven for jet lag; another found overall jet-lag ratings lower. They measured different things, so whether it helps sleep onset in particular is still open.

The decline was shown, not tested, and it runs alongside other changes: the later trials were larger, rated jet lag before the flight, or used a new scale. The 257 travellers had spent only five days away, so their body clocks had less to readjust on the way home. The reviewer who added the two null trials to the pool co-wrote one of them.

Every pooling of jet-lag ratings favours melatonin, but how much it helps turns on two later trials that found no benefit and were left out of the bigger estimates. Whether they were fair tests is disputed; no newer trial has settled it.

The crew's body clocks were already scrambled by back-to-back flights, so the early doses landed at varying body-clock times. Only the ratings recalled on day 6 separated the groups, while the daily ratings showed trends. A crew's working days are not an ordinary traveller's.

The only trial to compare start times found that beginning melatonin days before arrival did no better than placebo, while a pooling across trials leaned the other way. Whether a pre-flight start helps ordinary travellers is unsettled.

The trial reported which way each measure moved, not by how much. Nine people took each treatment, and three published papers all describe the same 27. The caffeine was a slow-release tablet, not coffee.

Both papers were written to explain a single conference report that had not been peer-reviewed. The letter proposing the blood-pressure route also says untreated insomnia could explain the same result.

With no comparison group and no count of people who took melatonin without trouble, the cases cannot give a rate. The link rests on timing and on recovery after stopping, with no formal causality score applied. Heart block is a rhythm problem, not heart failure.

Slow-release caffeine sped the hormones' return just as much in one of the studies. In a trial of 31 people whose days were full of irregular daylight, melatonin did not speed the body-temperature rhythm's shift. The two smallest studies, of 6 and 8 people, described no placebo group.