One dose did not change blood pressure in healthy adults
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.
What the study found
One dose of up to 30 mg left blood pressure where placebo left it
In 28 healthy adults given one dose of 10, 20 or 30 mg of phenylephrine or a placebo, pulse and blood pressure over 12 hours were similar on every dose, even as blood levels rose steeply with dose. A smaller study of a 10 mg cold remedy found no consistent effect either.
The caveat · Healthy volunteers, one dose each
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.