Can You Overdose on L-Lysine?

Lysine is an essential amino acid, which means your body cannot produce it — you must get lysine through your diet. Lysine supplements are often taken for cold sore outbreaks, but there's very little clinical research on lysine overdoses or the maximum lysine dosage for cold sores.

Most official sources hedge statements about lysine's efficacy for treating outbreaks of the cold-sore-inducing herpes simplex virus. And that's for good reason: Clinical evidence of lysine's efficacy is inconclusive at best.

As Harvard Health Publishing notes, in laboratory settings lysine hampers the activity of arginine, another amino acid that promotes the growth of herpes simplex virus. But an August 2015 Cochrane review found no consistent data to prove lysine's efficacy at preventing cold sores.

Still if you want to try taking lysine as a preventive measure, the University of Michigan notes that it's thought to be possibly safe when taken for up to a year.

Most sources recommend that if you are going to take lysine supplements, you should follow the manufacturer's dosage instructions on the bottle. The manufacturer may provide two dosage options: One for use as a general preventative, and another for use during acute outbreaks.

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If there's a possibility (albeit unconfirmed) that lysine might help with certain medical conditions, can this seemingly benign supplement hurt you? It might. The problem is that there is still relatively little research into how much lysine you should take, its possible side effects and any effect of an overdose.

The University of Michigan notes possible side effects of taking lysine supplements may include stomach pain and diarrhea. They also caution not to take lysine without medical advice if you take calcium supplements or medications that affect your gastrointestinal system.

But the absence of a clear intake limit (or, to put it another way, a clearly defined overdose amount) doesn't mean a supplement is automatically safe in any quantity. Neither does the seemingly benign label of "nutritional supplement." As the U.S. National Library of Medicine points out, you can even overdose on a multivitamin.

And as the U.S. National Library of Medicine's Toxicology Data Network explains, there have been scattered reports of adverse reactions including kidney dysfunction, hypertension and conflicting reports of lysine's effects on cholesterol levels. They warn that patients with kidney or liver disease shouldn't take lysine supplements.

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The University of Michigan offers further, excellent safety advice in regards to using lysine supplements. In particular, they note that:

• It is unknown whether lysine supplements are safe for pregnant or nursing people.
• Talk to a healthcare provider before taking lysine, especially if you have osteoporosis, kidney disease or lysinuric protein intolerance.
• Don't use multiple forms of lysine (e.g., liquid, tablets, etc.) together; this increases the risk of an overdose.

Finally, if you do choose to take lysine for a medical condition and said condition worsens or doesn't improve, talk to a doctor.

Reading through constant advice to consult a doctor before taking any new supplements might seem tiresome. But as already explained, supplements sometimes produce surprising interactions with prescription medications, medical conditions or other supplements.

Taking proactive care of your health is worth the bother of talking to a doctor, especially if you're thinking of taking lysine in quantities that leave you worried about an overdose.

As the University of Rochester notes, if you consume adequate protein in your diet, you'll get enough of the amino acids you need — including lysine. According to the Department of Health and Human Services, a healthy adult's diet should derive between 10 and 35 percent of its calories from protein.

With that said, if you want to adjust your diet to consume more lysine, the U.S. National Library of Medicine notes that particularly lysine-rich foods include red meats, fish, dairy products and wheat germ. Avocados are the only fruit or vegetable that contains notable levels of lysine.

Because the richest sources of lysine are in animal-based foods, if you're a vegetarian or vegan, consider talking to a doctor or nutritionist to ensure you're getting adequate lysine in your diet.