In this review published in 2019 authors evaluated the safety of L-lysine added to an ordinary diet in humans. Ultimately, 71 studies were selected for evaluation. Of these, 12 studies were of relatively high quality with Jadad scores ≥ 3. The dose range of L-lysine in the selected studies was 16.8-17,500 mg/day, and the range of dosing period was 1-1095 days. The observed adverse events were mainly subjective symptoms related to the gastrointestinal tract such as nausea, stomachache and diarrhea.
References:
Hayamizu, K., Oshima, I., Fukuda, Z., Kuramochi, Y., Nagai, Y., Izumo, N., & Nakano, M. (2019). Safety assessment of L-lysine oral intake: a systematic review. Amino acids, 51(4), 647–659. https://doi.org/10.1007/s00726-019-02697-3
