One dose changed digoxin not at all; ten days took a quarter off
Volunteers stabilised on digoxin took St John's Wort or placebo for ten days. Levels were unchanged after the first dose and 25 percent lower by day ten, and still widening.
What the study found
A single dose changed digoxin not at all, ten days took a quarter
Volunteers stabilised on digoxin took St John's Wort or placebo for ten days. After the first dose their digoxin levels were unchanged. By day ten they had fallen 25 percent against placebo, and the gap was still widening when the study stopped.
The caveat · Two time points, not a full curve
Twenty-five healthy volunteers split across two arms, single-blind, and none of them was taking digoxin for a heart condition where a quarter would come off a therapeutic target. Two measured timepoints establish the direction and rough timescale of onset rather than a curve.