Lysine is an essential amino acid, which means that the human body cannot synthesize it and must obtain it through food sources. Lysine aids in building muscle tissue, recovering from injury or surgery, and absorbing calcium effectively. It also helps the body produce antibodies, enzymes, and hormones. Lysine supplements are also sometimes used to treat outbreaks of the herpes virus.

Humans must consume 1-1.5 grams of lysine each day, either through the diet or through dietary supplements. Though lysine deficiency is rare, it can be serious, resulting in anemia, lethargy, hair loss, weight loss, loss of appetite, enzyme disorders, and growth and reproductive problems. Many animal and plant-based foods are rich in lysine. Fish, legumes, and cereal grains are among the best sources.

Clinical trials have shown lysine supplements to be effective in preventing recurrences of herpes outbreaks, and sometimes in lessening their duration. However, only fairly high doses, over 1000 mg and sometimes up to 3000 mg, are useful in this context. In addition, it has been speculated that another amino acid, argenine, may interfere with the effectiveness of lysine against the herpes virus.

For this reason, herpes sufferers using lysine supplementation are advised to lower their argenine intake and to keep their lysine to argenine ratio high. Dairy products are high in lysine and relatively low in argenine, while nuts are high in argenine and quite low in lysine. Therefore, nuts should be either eaten with cheese or avoided altogether by herpes suffers using this method.

Another problem with using lysine supplements to manage herpes is the possible negative side effects associated with regular high doses of lysine. Gastrointestinal distress and renal impairment can both result from excessive lysine intake, such as that suggested for herpes patients. Lysine supplements in high doses are not recommended for those with compromised renal function or risk factors for liver or kidney disease. Most doctors recommend taking lysine only when herpes outbreaks are imminent, rather than on a regular basis.