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.
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