L-Lysine: Benefits, Side Effects, Best Time to Take It & More

L-Lysine

(Lysine)

Evidence: Reasonable
Possible Benefits: Low
Safety: High

What is L-lysine?

Lysine is one of 9 essential amino acids. Our bodies cannot synthesize this amino acid but we need it to survive. As a supplement, L-lysine is often used for improving muscle growth and exercise performance but it isn’t very effective in this regard. This article is about the main benefits of L-lysine, its potential side effects, the best time to take it, and more.

What does L-lysine do for the body?

Lysine is an essential amino acid, which means the body needs it to survive and cannot synthesize it.

This amino acid serves as a building block for many proteins in the body.

Lysine interacts with arginine in many ways and should be kept in balance unless you have a strong reason to off-balance them (such as herpes simplex). Taking too much of one can override the functions of the other. For example, high doses of lysine could hinder the ability of arginine to produce nitric oxide.

Possible benefits

It is important to note that all of the potential benefits mentioned below are dose-dependent. Generally, the higher the dose, the more pronounced the effects are. However, they do reach a plateau at a certain point. We will discuss the best dosing protocol later in this article.

Major benefits

Correcting a lysine deficiency – Since lysine is an essential amino acid, the body needs at least some amount to survive and function properly. Fortunately, not getting enough lysine is extremely rare but not getting enough can lead to multiple health problems, such as impaired fatty acid metabolism, anemia, and systemic protein-energy deficiency. This shouldn’t happen unless you consume very low amounts of protein.
Reduced symptoms of herpes simplex – Lysine supplements can override and block the absorption of arginine. Arginine is considered a nutrient for HSV and promotes its replication while lysine prevents replication. If you suffer from herpes, try supplementing with 2 or more grams of L-lysine.

Minor benefits

Reduced anxiety – This benefit only applies if you combine L-lysine with L-arginine. The combination is very effective at reducing state and trait anxiety. It may also reduce generalized anxiety disorder (GAD) but science is not yet clear on that. For best results, take 2.5 grams of each amino acid daily spread into 2 or more doses.

Possible side effects

These side effects are dose-dependent. The risk for them increases (often linearly but sometimes exponentially) as you increase the dose. Some of the side effects only apply to very high doses.

Amino acid imbalance – All essential and non-essential amino acids need to be kept in balance as they act synergistically in many ways. Too much of one amino acid can sometimes cause side effects without enough of another amino acid. That is most notably the case for glycine and methionine, but the principle applies to other amino acids, such as lysine and arginine, and the BCAA trio. Using a single amino acid supplement may lead to a negative nitrogen balance, which can lessen how well your metabolism works. A protein powder is usually a better choice for getting enough amino acids unless you have a specific goal in mind targeted by a specific amino acid/s.
Lysine toxicity – While acute toxicity has never been reported, taking high amounts of L-lysine could lead to chronic toxicity over time and cause some health problems, often related to arginine deficiency. Taking over 10 grams per day can also lead to diarrhea and intestinal distress but these symptoms usually go away when one stops taking lysine. To prevent chronic toxicity, it is best to stay below 2 grams a day unless you have a great reason to take more.
Contamination – Contaminated supplements are uncommon in the USA and other well-regulated countries. However, if you wish to buy products from China, India, or other countries without strict regulations, beware that the supplements may be contaminated. Either way, you need to choose the brand you order from wisely. It is highly recommended to check the certificates or read through some reviews for the specific product before you buy it. The FDA (Food and Drug Administration) has the power to regulate dietary supplements but can only do so after they have been on the market for a while. That’s because supplement companies are not obligated to announce to the FDA when releasing a new product on the market. The FDA has to discover the product and test it for potential impurities, which can take a lot of time. During that time, the supplement can be sold on the market even if it’s impure. Also, supplement companies can change their manufacturers without announcing it to the FDA.

Who should not take L-lysine?

You should probably avoid taking the supplement if you:

eat high amounts of protein from food (most whole foods contain at least some amount of each essential amino acid)
are deficient in arginine
experience a severe adverse reaction after taking the amino acid
are on a tight supplement budget (since there are more cost-effective supplements on the market for most people)

Who will benefit the most?

You should consider taking the supplement if you:

suffer from herpes simplex
supplement with L-arginine
consume too low amounts of protein (less than 0.3 grams/pound of body weight)
are on a plant-based diet but don’t eat legumes
are muscular and work out a lot
have a high budget for supplements (assuming the supplement doesn’t contain impurities, it is safe for most people when taken at regular doses and shouldn’t do more harm than good)

How much L-lysine should you take?

The RDA (recommended daily allowance) for this amino acid is 38 mg/kg/day for all adult men and most adult women. This is enough for the majority of people to prevent any symptoms of deficiency.

The RDA increases to 41 and 56 mg/kg/day for pregnant and lactating women, respectively.

Since this amino acid is in almost every food, you probably already get sufficient amounts from food alone. About 0.36 grams of protein/pound of body weight should be enough to prevent a deficiency.

If you take L-lysine to reduce the symptoms of herpes simplex, 2 grams appears to be the best daily target for most people.

If you take this amino acid to reduce anxiety, pair 2.5 grams of L-lysine with 2.5 grams of L-arginine. These amounts should provide most of the benefits without meaningful side effects.

The upper safety limit for this amino acid is not well-established. To stay on the safe side, don’t take more than 2.5 grams daily unless you have a great reason to do so. Always pair L-lysine with a similar amount of L-arginine unless you suffer from herpes. Higher amounts than 2.5 g/d may cause problems if you take the supplement for a prolonged period.

Food sources of lysine

Lysine is found in all whole foods that contain dietary protein.

The amount of lysine per gram of protein varies from food to food but a general rule of thumb is that the more protein you eat, the more lysine you are getting from food.

If you are on a plant-based diet, it is best to add some legumes to make sure you are getting enough lysine.

The easiest way to find out exactly how much lysine or other amino acids you are getting from food is with Cronometer.com. This free app allows you to track all vitamins, minerals, and more.

Best time to take L-lysine

Like most other amino acids, L-lysine is water-soluble, so you don’t have to take it with food to absorb it well. Taking the supplement with food is better if it causes stomach upset when you take it on an empty stomach.

To maximize the benefits, take L-lysine and other amino acids before or after a workout.

Whether you take the supplement in the morning or the evening doesn’t matter. It should not interrupt your sleep in any way.

If you practice time-restricted eating, take this amino acid during your eating window to guarantee it doesn’t break your fast.

Unless it feels too impractical, spread the daily dose into 2+ smaller doses throughout the day.

Interactions

L-arginine
This combination is highly effective for reducing many types of anxiety, state and trait anxiety in particular. Combining these two amino acids may and may not be effective for generalized anxiety disorder (GAD). To maximize this benefit, it is best to take L-arginine and L-lysine together and take 2.5 grams of each daily. Beware that taking these two together may negate the benefits of L-lysine related to the treatment of herpes simplex.
Other amino acids
All essential and non-essential amino acids need to be kept in balance as they act synergistically in many ways. Too much of one amino acid can sometimes cause side effects without enough of another amino acid. That is most notably the case for glycine and methionine, but the principle applies to other amino acids, such as lysine and arginine, and the BCAA trio. Using a single amino acid supplement may lead to a negative nitrogen balance, which can lessen how well your metabolism works. A protein powder is usually a better choice for getting enough amino acids unless you have a specific goal in mind targeted by a specific amino acid/s.
Calcium
L-lysine slightly increases the absorption of calcium.

Where to buy L-lysine

Amazon is the best option for ordering L-lysine supplements in most countries. They offer some very affordable products backed by many positive reviews. Also, you can choose from a wide range of brands without having to search through other markets on the internet.

Beware some brands display the dosage per serving instead of per pill or capsule. Therefore, you may accidentally buy something less potent than you intended. Do not fall for this marketing trick.

FAQ

You can take the supplement daily and do not need to cycle it. However, it is certainly not a problem if you don’t take it daily. Not taking the supplement every once in a while could lead to better absorption. That is yet to be proven or disproven.

All of these options are fine. The two most important things to consider are the price and dosing. Powders are almost always the cheapest form. However, you may need a highly accurate scale to dose them correctly (preferably 0.001g). You can get one for as little as $20 from Amazon. Dosing the powders also takes some time that can add up over months or years. The disadvantage of capsules is that they often contain bovine gelatin, which rarely comes from an ethical source.

Yes. Most amino acids, including L-lysine, absorb and digest well if you take them before falling asleep. The supplement should not impact sleep quality in any significant way.

This amino acid should not become harmful once it exceeds the expiration date but can lose potency over time.

Keep the supplement in a cold, dark, and dry place, and it should remain just as potent for many months or even years.

While toxicity is rare, too much lysine in the system can cause some health problems, often related to reducing the absorption and availability of L-arginine. It is best to stay below 2.5 grams a day to prevent these side effects.

You may need more of this amino acid if you:
– don’t eat enough protein (less than 0.3 grams/pound of body weight)
– are on a plant-based diet but don’t eat legumes
– are muscular and work out a lot
– suffer from herpes simplex
– supplement with L-arginine

The half-life of lysine in the body is about 15-20 minutes. This amino acid only stays in your system for a few hours after you ingest it.

In the long term, you need to take the supplement for about 2-4 weeks to begin noticing the benefits.

Amino acid supplements often come from animal products, but they do not have to be since all whole plant foods contain all essential amino acids. You can easily find vegan-friendly L-lysine powders but always check the label to be sure. If you buy the amino acid in a capsulated form, beware that the capsules often contain animal-based gelatin. Instead, find a brand that puts its products into cellulose capsules.

Like most other amino acids, lysine is water-soluble, so you don’t have to take it with food to absorb it well.

While low doses may not break a fast, higher doses certainly can. If you practice time-restricted eating, take this amino acid during your eating window so it doesn’t break your fast.

References

Most of the information provided in this guide is supported by scientific research that can be found and verified in the PubMed medical library. We highly encourage you to use the library to verify anything said in this article. We excluded from consideration studies that are either confounded or have a high conflict of interest.

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