★★☆Single study — solid evidence, such as one good trial or a large observational dataset, but not replicated at the top tier.
The marker compound varied widely between brands, and batch to batch
Chemists measured both marker constituents in eight St John's Wort products across five batches of each. The products are not interchangeable.
What the study found
Same brand, different batch, different amount of the marker compound
Chemists measured both marker constituents in eight St John's Wort products across five batches of each. Amounts differed widely between brands even after correcting for how much extract a dose contained, and some brands varied markedly batch to batch. The products are not interchangeable.
The caveat · Wide, but never put in numbers
The published abstract reports the pattern without the numbers, so this establishes that the variation is large without saying how large. The products were bought on the German market in 2001, and nothing here describes what is manufactured today.