L-Lysine (or Lysine) is an essential amino acid for humans and is important for proper growth  and tissue repair . It also plays an important role in the production of carnitine (nutrient responsible for converting fatty acids into energy) . Most people get enough lysine in their diet, although athletes may need more. It is also taken by mouth to improve athletic performance.
Foods rich in protein are good sources of lysine.
That includes :
- red meat,
- pork, and poultry,
- fenugreek seed,
- certain fish,…
Dosage and RDA
Dosing has not been adequately studied, but beneficial clinical effects occur in doses ranging from 100 mg to 4 g a day. Higher doses may also be useful, and toxicity has not been reported in doses as high as 8 g per day. 
For adults ages 13 and older the recommended daily allowance is 12 mg/kg/day.
Benefits for Exercise
Muscle mass is determined by protein synthesis and protein degradation. Lysine (Lys) is considered to be essential for maturity in growing as animals fed with low-Lys diets were growing more slowly than those fed standard diets . After changing to Lys sufficient diet, hormone levels changed which resulted in increased protein synthesis and suppressed protein degradation of skeletal muscles. Other animal studies  have also shown that oral administration of Lys to rats suppressed the rate of muscle protein degradation. Sato et at.  reported that Lys suppresses muscle protein degradation via the activity of autophagic–lysosomal system in part through the activation of mTOR and Akt in C2C12 myotubes.
Lysine and Arginine
We have talked before about L-arginine and its effects on growth hormone release in combination with exercise and at rest. In this section, we will discuss the combination of L-Lysine and L-Arginine on human growth hormone (hGH) release. Suminski et al.  tested their effect in 4 trials in sixteen young healthy men. Trial 1 performed exercise and ingested placebo, trial 2 ingested 1,500 mg L-arginine and 1,500 mg L-lysine immediately followed by exercise, trial 3 same as trial 2 only without exercise and trial 4 no exercise and placebo. No differences in growth hormone levels were noted between the exercise trials. Growth hormone was increased in trial 3 where amino acids were ingested without exercise. Another study supplemented with 1,200 mg of L-lysine and 1,200 mg of L-arginine increased human growth hormone levels within 30 minutes and peaked after 90 minutes with its human growth hormone concentrations elevated up to 8 times greater than basal levels . When 11 competitive weightlifters (aged 19-35) were supplemented with combined L-arginine, L-ornithine, and L-lysine twice a day (2 grams each) there were no significant differences between serum human growth hormone levels on 24-hour level . So, it seems that low dose amino acid supplementation provides no ergogenic value.
Exercise alone is a powerful human growth hormone secretion stimuli and these amino acids don’t seem to increase it further. However, at rest, they seem to increase growth hormone significantly.
Many bodybuilders consume amino acids before strength training in a belief that this will increase exercise-induced growth hormone release. We found no appropriately conducted study that would show that oral supplementation with amino acids prior exercise would further increase growth hormone levels.
Interestingly lysine competes with arginine for absorption and entry into cells .
Herpes Simplex Virus (HSV) – Cold Sores
Cold sores (or fever blisters) are caused by the herpes simplex virus (HSV) . Lysine appears to be an effective agent for reduction of occurrence, severity and healing time for recurrent HSV infection. 312–1,200 mg of lysine daily accelerated recovery from herpes simplex infection and suppressing recurrence in 45 patients with frequently recurring herpes infection . Another double-blind, placebo-controlled, multicenter trial by Griffith and colleagues  also reported fewer infections and significantly diminished severity and healing time. The possible mechanism of its inhibition of HSV growth is by knocking out arginine .
There is one case report suggesting lysine may ameliorate angina 
Precautions and Side Effects
L-lysine in a diet is considered safe. Even relatively high oral doses of lysine are likely to be safe . Minor side effects such as diarrhea, nausea, and abdominal pain, have been reported with lysine ingestion .
(Other common names: Lysin, L-Lysine Hydrochloride / Monohydrochloride / Acetylsalicylate, L-Lysine HCl, Lysine Acetate, Enisyl, (S)-2,6-Diaminohexanoic acid, L-2,6-diaminohexanoic acid)
- University of Maryland Medical Center. “Lisine” Retrieved from http://www.umm.edu/ at 21. May 2013
- Suminski, R. R., et al. “Acute effect of amino acid ingestion and resistance exercise on plasma growth hormone concentration in young men.” International journal of sport nutrition 7.1 (1997): 48.
- Isidori, A., A. Lo Monaco, and M. Cappa. “A study of growth hormone release in man after oral administration of amino acids.” Current medical research and opinion 7.7 (1981): 475-4.
Fogelholm, G. M., et al. “Low-dose amino acid supplementation: no effects on serum human growth hormone and insulin in male weightlifters.” International journal of sport nutrition 3.3 (1993): 290-297.
- Wolters Kluwer Health. “Lysin”. Retrieved from Drugs.com at 7. Jan 2014
- https://ncit.nci.nih.gov/ncitbrowser/ConceptReport.jsp?dictionary=NCI_Thesaurus&ns=NCI_Thesaurus&code=C29171 Retrieved 17. Mar 2017
- Griffith, RichardS, et al. “Success of L-lysine therapy in frequently recurrent herpes simplex infection.” Dermatology 175.4 (1987): 183-190.
- Griffith, Richard S., Arthur L. Norins, and Christopher Kagan. “A multicentered study of lysine therapy in herpes simplex infection.” Dermatology 156.5 (1978): 257-267.
- http://www.hmdb.ca/metabolites/HMDB00182 Retrieved 17. Mar 2017
- Ishida, Aiko, et al. “Muscle protein metabolism during compensatory growth with changing dietary Lys levels from deficient to sufficient in growing rats.” Journal of nutritional science and vitaminology 57.6 (2010): 401-408.
- Sato, Tomonori, Yoshiaki Ito, and Takashi Nagasawa. “Regulation of skeletal muscle protein degradation and synthesis by oral administration of Lys in rats.” Journal of nutritional science and vitaminology 59.5 (2012): 412-419.
- Sato, Tomonori, et al. “Lysine suppresses protein degradation through autophagic–lysosomal system in C2C12 myotubes.” Molecular and cellular biochemistry 391.1-2 (2014): 37-46.
- Pauling, Linus. “Case report: Lys/ascorbate-related amelioration of angina pectoris.” J. Orthomolecular Med 6 (1991): 144-146.
- http://www.webmd.com/skin-problems-and-treatments/tc/cold-sores-topic-overview Retrieved 18. Mar 2017