A 28-day oral toxicology study of an aqueous extract of Polypodium leucotomos (Fernblock®)

•The NOAEL study was 5000 mg/kg bw/d-the highest dose tested.•No target organs or treatment-related toxicological effects were identified.•Our results are relevant to the evaluation of the safety of human ingestion of Fernblock®.

Fernblock® is a standardized commercial aqueous extraction of the leaves of the tropical fern Polypodium leucotomos promoted as an orally active photoprotective substance. In a previous battery of toxicological tests on Fernblock®, no genotoxicy was observed and no oral toxicity was observed up to 1200 mg/kg bw/day. The current study was conducted in Hsd.Han Wistar rats using doses of 0, 2000, 3500, and 5000 mg/kg bw/day Fernblock® by gavage for 28 consecutive days. No mortality or toxic effects were observed and no target organs were identified. The no observed adverse effect level was determined to be 5000 mg/kg bw/day, the highest dose tested.