Decongestant
The decongestant in DayQuil and Sudafed PE. Swallowed, it did no better than placebo in modern hay-fever trials, and the FDA has proposed dropping it.
Phenylephrine hydrochloride (the salt sold in oral tablets and liquids; 10 mg per adult dose in US OTC products); older and chemical names: m-synephrine, metasynephrine, metaoxedrine, mezaton, Neo-Synephrine (historic brand, now mainly a nasal spray). The oral decongestant in Sudafed PE and in multi-symptom cold products such as DayQuil and NyQuil Severe (the "PE" suffix marks it). NOT a synonym: pseudoephedrine, the older oral decongestant sold from behind the pharmacy counter in the US, which PE products replaced; synephrine (p-synephrine, bitter orange), a related but different amine. Brand names are written here as a deduplication aid and are not reader-facing facts without a cited source.
A 2025 search for trials of oral decongestants taken daily for 7 days or more found none of phenylephrine that measured blood pressure.
For the other oral decongestants pooled in that search, a week or more of daily use changed systolic pressure by 0.91 mmHg on average, at very low certainty. None of those trials used phenylephrine, so the figure cannot be carried over to it.
In one week-long hay-fever trial, doses up to 40 mg every 4 hours eased congestion no more than a placebo did.
The trial's own title calls it open-label, so people may have known what they were taking. That usually inflates a self-rated benefit rather than hiding one. Everyone in it had hay fever, not a cold.
In four trials in people with hay fever, from one dose to a week of use, congestion eased no more on phenylephrine than on a dummy pill.
All four trials were in hay fever, so none tested a blocked nose from a cold. Two of them gave a single dose and followed congestion for 6 hours. The largest used a 30 mg slow-release tablet, not the 10 mg tablet sold in cold remedies.
In single-dose studies of healthy adults, 1,000 mg of acetaminophen with 10 mg of phenylephrine raised blood levels about 2.1-fold. Relief was not tested.
More phenylephrine in the blood is not shown to mean a clearer nose: no study tested whether the pairing relieves congestion better. The studies gave single doses to healthy volunteers. Their authors work for a company that makes combination painkillers.
The only study in congested children, 41 aged 2 to 17, measured blood levels after one dose, not relief. The DayQuil label is written for ages 4 and up.
The review's young-children finding covers cold remedies with mixed ingredients, most of them other decongestants, so it is not phenylephrine's own result. The children absorbed the drug much as adults do, with somewhat lower peak levels.
All four modern placebo trials were in hay fever. Cold trials test multi-ingredient remedies, which ease some symptoms without showing what phenylephrine adds.
The one modern placebo trial begun in real colds was stopped early for low enrolment and never published in a journal. Older single-dose laboratory studies, from the 1950s to 1970s, were never published either.
Standard DayQuil Cold & Flu gives 10 mg of phenylephrine per adult dose, its only ingredient for a blocked nose. DayQuil Intense Flu contains none.
A label lists what the maker is permitted to claim under US rules, not proof that the claim holds. Labels change, and this one took effect in June 2026.
In September 2023, all 16 voting advisers found that current data do not show the labelled oral dose works as a decongestant. Safety was not the question.
An advisory vote is advice to the FDA, not a ruling; the agency decides separately. Members noted that no data measure the drug in the nasal lining.
The FDA proposed removing it as an over-the-counter decongestant in November 2024. In September 2026 the order was still only proposed, so products using it stay on sale.
The status is dated: it reflects the FDA's order page on 26 September 2026. The proposal concerns effectiveness, not safety. It covers phenylephrine taken by mouth, not nasal sprays.
Taken by mouth, phenylephrine is extensively converted in the gut wall, and FDA advisers saw that low uptake as consistent with trials finding no relief.
No study has measured phenylephrine in the lining of the nose, where it would have to act. So the link between little drug in the blood and no relief is inferred, not shown.
Case reports describe systolic pressure rising more than 60 mmHg in people on MAO inhibitors, and the US tablet label forbids taking the two together.
These are reports of individual cases gathered in a narrative review, so they show that it can happen, not how often.
In 28 healthy adults, single doses of 10 to 30 mg left pulse and blood pressure over 12 hours similar to placebo. People with high blood pressure were not tested.
Both studies gave single doses, so neither shows what a day or a week of doses does. Everyone in them had normal blood pressure. The larger study was run by employees of a phenylephrine maker. A model built from eye-drop data predicts a larger rise when 10 mg is taken with 1,000 mg of acetaminophen, 12.3 against 4.2 mmHg in average arterial pressure, a prediction nobody has measured.
From 2012 to 2021, pharmacies bought 19.8 billion units of phenylephrine products against 13.2 billion of pseudoephedrine, and all but 21 of 732 phenylephrine products were mixes.
Units count each tablet or 5 mL of liquid, not courses of treatment. Stores without a pharmacy, such as gas stations, are not counted.
One dose each, in 39 people with hay fever in a pollen chamber: pseudoephedrine 60 mg eased congestion over 6 hours, and phenylephrine 12 mg did no better than placebo.
Each person took all three in turn, and the authors flag that earlier doses may have carried over: in the first round alone, phenylephrine's gap over placebo was 64% of pseudoephedrine's, against 17% across all rounds. It tested a single dose. The congestion came from pollen, not a cold.
Of 18 published cases of ischaemic colitis after an oral decongestant, 3 involved phenylephrine, and all 18 recovered. Case reports cannot show the drug caused it.
Case reports cannot show that the decongestant caused the colitis. Unusual cases are the ones that get written up and published. With 3 phenylephrine cases, no rate can be worked out.
No findings tagged to that goal.
Search runs entirely in your browser. Nothing you type is sent anywhere.