Supplement company NOW recently completed another round of testing dietary supplements purchased on Amazon, this time on the herb St. John’s Wort.

According to the company, every single product failed potency testing, and several samples contained synthetic dyes, which are commonly used by bad actors to make low-quality or adulterated products appear authentic.

St. John’s Wort (Hypericum perforatum) is used to support mood and emotional well-being. The key active compounds hypericin and pseudo hypericin are responsible for its benefits, and are typically standardized to concentrations of 0.3% in supplements.

To test the products, NOW purchased two bottles of each, including two bottles of its own St. John’s Wort, from Amazon.com in August. A bottle of each sample was tested in one of NOW’s in-house labs, while another sample was sent to Alkemist Labs, an ISO 17025-accredited independent laboratory specializing in botanical identification and testing.

Hypericin was evaluated by high-performance liquid chromatography (HPLC), using a reverse-phase method after irradiation with white light to ensure specificity. Hypericin content was expressed as the sum of hypericin and pseudo hypericin. High-performance thin-layer chromatography (HPTLC) was performed to confirm product identity and detect common synthetic dyes such as Brilliant Blue (E133), Sunset Yellow (E110), and Tartrazine (E102). In less specific testing methods, these dyes artificially inflate hypericin readings, NOW reported.

Across 22 brands, only NOW’s products met total label claim for hypericin, and contained no synthetic dyes. Nine brands contained synthetic dyes, five brands had no detectable hypericin, and all gummy products lacked detectable hypericin. St. John’s Wort, as a whole herb, may have hypericin content as low as 0.03%, and of the six products which contained non-standardized material, all had less than this amount.

“We are accustomed to seeing abysmal test results in at least some of the brands we buy from Amazon for this testing program, but this time we were shocked to find that they all failed, and only NOW St. John’s Wort met the label claim for total hypericin and showed no evidence of dye adulteration,” said Katie Banaszewski, senior director of quality at NOW. “What stands out most to me is the strong evidence that none of these brands used fit-for-purpose testing, if they tested at all. Our in-house analytical testing, paired with Alkemist Labs’ independent verification, underscores the importance of scientifically valid methods.”

NOW noted that specific testing methods are critical for testing this botanical, as methods like colorimetric or spectrophotometric assays can be fooled by synthetic dyes that mimic the red color of hypericin. HPLC can separate and identify true hypericin compounds from adulterants, on the other hand.