Sleep better

That 9-hour figure is an average across many doses and timings, not a personal cut-off. How fast a person clears caffeine varies widely, partly for genetic reasons, so the same cup at the same hour lands differently on two people. Older adults' sleep tends to be more sensitive to it than younger adults'.

Eighty-four separate comparisons across 23 conditions means some significant findings are expected by chance, and most were graded low or very low quality. The missing cannabidiol effect on pain is an absence of evidence inside these trials, not a tested null.

This measures anticholinergic burden as a whole, not diphenhydramine and not antihistamines. Only 8 of the 25 studies found could be pooled at all. The scales used to score that burden agree poorly with one another, so what is being measured is not the same thing from study to study.

The trial was powered on the diary outcome, so a flat recording is a difference not detected rather than a difference shown to be absent. Mild insomnia in adults averaging 44, not the older people the warnings are about. The drug arm ran 14 nights, so nothing here reaches beyond a fortnight.

This comes from the same forty drivers and the same four sessions, so it inherits that setting: a simulator, a daytime dose, driving one hour later. A failure of self-rating to predict performance across one hour-long test is not proof that people can never judge their own impairment.

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The trial registry lists two melatonin trials in heart failure, one withdrawn and one with no update since 2020.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.

This was whole matcha, theanine and catechins and caffeine together, so no result here belongs to theanine specifically. The two results that moved were secondary outcomes, which carry less weight than the ones the trial was built to test. And everyone in it already had cognitive decline, which is not a healthy adult drinking green tea.

Every outcome here is what people reported about their own sleep; nothing was recorded by a wrist monitor or in a sleep lab. Few of the pooled trials tested theanine on its own rather than mixed with other ingredients, so its individual share stays blurred. And the authors say the best dose and duration are still undetermined.

A pilot of thirty people cannot rule out a small effect. One objective measure did move — sleep efficiency favoured cannabidiol at week two — while every measure the sleepers reported themselves did not. And 150mg nightly is about three times what people typically take.

The authors describe the effects as small. Everyone measured was young and healthy, at an average age of 20, so this says nothing about older adults or about anyone with a sleep or stress disorder. And these are the same people watched over time rather than an experiment, so something else in their days could be driving both ends.

These were tiny experiments, 13 men in one of them, run over one or two nights. All the participants were young men, so nothing here covers women or older adults. And a night or two of lost sleep is not years of it, so how far the flattening goes over a lifetime is unmeasured.

This is what one US label states, not a measurement of harm. Nothing here counts how often people do stack a second acetaminophen product on top, only that the label names it as the thing to avoid.

The two milligram figures are worked out from published molecular weights rather than quoted from a label, so they are close but should not be treated as an exact conversion factor. Both label versions were read on 6 September 2026, and printed strengths do change.

The source is a clinical reference chapter summarising other work rather than a study. It names these effects without giving a rate for any of them, so this says what the drug does at ordinary doses, not how likely each is in a given person.

A panel of experts weighs evidence and then votes, so strong records a committee's confidence rather than an effect size. The list carries its own exception: treating a severe allergic reaction may still be appropriate. The harms bundled into one line run from dry mouth to contested dementia evidence.

The instruction sits on the allergy liquid. The dedicated sleep aids handle the question differently, by excluding anyone under 12 outright, so the sentence belongs to this label, not to diphenhydramine labelling in general. A label requirement is not evidence about how often harm follows.

Twenty-one people, about seven per group, with standard deviations of 4.2, 2.5 and 1.8 hours around those means. The dose was 1.25 mg per kilogram, roughly 86 mg in the adults, well above the 25 to 50 mg a tablet gives. A separate trial at 25 mg found no age difference at all, most likely because of that gap.

A label count is not a product count and not a measure of how many people take these. The same physical product carries several records across repackagers and store brands, so duplicates sit inside that figure. Counts drift as labels are added and withdrawn, which is why the date belongs with the number.

A label records what a regulator permits a company to print, not what the evidence shows. The dependence claim is narrowly defensible: diphenhydramine is not a controlled substance, and the one trial that looked found no rebound insomnia on stopping. This is one product from one manufacturer in one country.

These are calls to a poison centre, so mild poisonings nobody phoned about are missing and the mix looks worse than all ingestions would. The amount swallowed is what someone reported afterwards, unreliable in both directions. Above 1.5 g, coma and seizures grew more common while delirium did not.

The search deliberately began at 2003, so three is a count inside that window rather than of the whole literature. One database was searched. The second author worked for a company selling over-the-counter sleep products, melatonin among them, though its own diphenhydramine line comes off badly too.

Fifteen healthy men, no women, nobody with a sleep problem. The dosing was twice daily and the outcome was daytime sleepiness, so a nightly bedtime habit is an inference rather than something this trial watched. Four days shows tolerance arriving and says nothing about weeks.

The 300 mg figure comes from a clinical reference chapter for the allergy indication, not from an over-the-counter label, so quoting it about sleep would misdescribe what those products allow. The 50 mg figure is read off one US sleep-aid label, and other markets word their limits differently.

The label tells users not to drive while taking it and says nothing about the following morning, which is where the driving evidence sits. One product from one manufacturer in one country.

This was read off US label records on 6 September 2026, for one brand family. Brand compositions change, and a product carrying the same name in another country may contain something else again.

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.

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 dose was daytime, with driving an hour later, the reverse of the bedtime-then-morning pattern a sleep aid creates. On reaction time to a car blocking the lane, alcohol was slowest, so worse than alcohol holds for the measures the paper led with, not every one. The comparator's maker funded the trial.

Fifty milligrams of diphenhydramine impaired driving more than alcohol at roughly the legal limit, and 25 mg looked like placebo. Both are sold as normal doses, so what separates them is a step between two amounts, not a dispute about one.

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 participants skewed middle-aged and older, and most were women. A long list of outcomes was tested at once, which on its own makes some of the positive ones likely to be chance.

One small crossover trial in young women only, so nothing here covers men, older adults or anyone especially sensitive to caffeine. The 30mg of caffeine is well under a standard cup of coffee at roughly 95mg, which leaves the everyday dose untested. The lead author is affiliated with a commercial tea company.

This is an absence of detected difference, not a measured absence of effect. Thirty-seven people in a crossover design has limited power and the abstract states no power calculation. A single dose in volunteers with no sleep complaint, so nothing here speaks to taking it every night.

What would settle this is one study testing 25 mg and 50 mg of diphenhydramine side by side, and nobody has run it. Until then, where between the two doses impairment begins is unknown.

The authors do not say the misuse is harmless, only that the self-harm cases carried the worse outcomes. Intent is coded by whoever takes the phone call, and the line between misuse and a suicide attempt is drawn there. The warning itself would have lifted reporting.

The English null is wide: a real 20 to 30% increase sits inside its range. The Taiwanese comparison group is small, 36,081 non-users against 677,971 users, and people with hay fever who take nothing are unlikely to resemble those who do. Neither design separates the drug from the reason it was taken.

Whether antihistamines raise dementia risk is unsettled. English prescription records show no significant link, Taiwanese dispensing records a rise with dose, and English records miss most shop-bought use, so neither can correct the other.

The conditions these drugs treat, insomnia and low mood among them, are early signs of dementia themselves, so the drug may be marking the illness rather than causing it. Dropping the last twelve months of use blunts that without removing it. One health system in Seattle, shop-bought use only partly captured.

The dose, 76 mg of the citrate salt, is an ordinary amount in an unfamiliar unit, matching the 50 mg of hydrochloride a sleep aid delivers. Under the prespecified testing plan, the remaining comparisons were non-significant or ineligible to test. A competing product's maker designed and part-authored it.

No p-value is given for diphenhydramine against placebo on braking, so the 29 millisecond gap between them cannot be called significant. Both significant braking comparisons involve the sponsor's own drug. Lane wander is a validated road-test measure and still a proxy for crash risk, not crash risk itself.

The road test adds what a simulator cannot: 50 mg of diphenhydramine made drivers weave on a public road. It tested only 50 mg, so it cannot say whether 25 mg, which matched placebo in another trial, impairs driving.

A call rate is not an event rate, and reporting habits shifted across those twelve years. The percentages come without the counts behind them, so a 263% rise from a small base may be a small absolute change. Nothing here measures how much diphenhydramine was being taken, so none of it can be read per user.

A pattern shared by drugs that do and do not reach the brain points somewhere other than the drug. More medicine dispensed means more medical contact and more chances for a diagnosis to be recorded, and heavier users are sicker to begin with. The authors call for trials to confirm any association.

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.

A secondary outcome is exploratory unless it was named in advance and corrected for testing many things at once, and this paper reports no such correction. Three of the four authors work for Meiji Holdings, which sells NMN. The authors highlight that walking-time changes tracked changes in blood NAD, 2PY and 4PY, which is an association inside one trial rather than evidence that raising NAD caused the walking.

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.