Diphenhydramine

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.

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.

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.

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.