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★★★Well replicated — this finding’s sources average out to meta-analyses, systematic reviews or high-powered trials.
Phenylephrine did no better than placebo for a blocked nose
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.
What the study found
Congestion eased no more on phenylephrine than placebo in four trials
Four modern trials, from one dose in a pollen chamber to a week of use in 575 people, all came out the same: congestion eased no more on phenylephrine than on a dummy pill. The swallowed decongestant sold for a blocked nose did not beat placebo in any of them.
The caveat · Hay fever, not colds
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.