Lysine is an amino acid, one of the building blocks of protein. As a supplement (L-lysine) it is taken mainly to prevent or treat cold sores and other herpes simplex outbreaks.
Also known as: L-lysine, lysine hydrochloride, L-lysine HCl.
A placebo-controlled trial used 400 mg three times a day (DiGiovanna 1984). A 2017 review describes studies of under 1 g to more than 3 g a day (Mailoo 2017). These are study protocols, not a recommendation.
It is sold in the US as a dietary supplement. Under the 1994 dietary supplement law (DSHEA), FDA does not approve dietary supplements before they are marketed, and the maker, not FDA, is responsible for safety and labeling.
What studies show: a 2015 Cochrane review of interventions to prevent cold sores found no evidence that lysine works (Chi 2015). In a placebo-controlled trial of 21 people with frequent herpes outbreaks, lysine 400 mg three times a day did not reduce how often, how long or how badly outbreaks happened (DiGiovanna 1984). A 2017 review concluded that lysine under 1 g a day appears ineffective without a low-arginine diet, that over 3 g a day appears to improve people's own ratings of their outbreaks, and that longer controlled studies are needed (Mailoo 2017).
Safety: the 2017 review says people with heart or gallbladder disease should be told of theoretical risks of lysine supplements (Mailoo 2017). The Cochrane review found that long-term prescription antiviral pills can prevent cold sores, with a small benefit.
We could not find a single published half-life or time to peak for lysine that applies to a supplement dose, so we do not list one.
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