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

L-Ornithine-L-Aspartate

(L-Ornithine + L-Aspartic Acid)

Evidence: Reasonable
Possible Benefits: Reasonable
Safety: High

What is L-Ornithine-L-Aspartate?

L-Ornithine-L-Aspartate is a 50/50 mixture of L-ornithine and L-aspartic acid, two non-essential amino acids that naturally come from food or get synthesized in the body. As a supplement, most people use it for improving exercise performance, fertility, and testosterone levels. This article is about the main benefits of L-ornithine-L-aspartate, its potential side effects, the best time to take it, and more.

What does L-ornithine-L-aspartate do for the body?

Since both L-ornithine and L-aspartic acid are non-essential amino acids, you do not need to consume them to survive. However, these amino acids still play a significant role in human health.

Along with L-arginine and L-citrulline, ornithine is an intermediate in the urea cycle, a cycle of biochemical reactions that produces urea from ammonia.

Ornithine can convert in the body to L-citrulline and citrulline can indirectly convert into L-arginine, which means the amino acid has many effects beyond the direct effects of ornithine.

The body uses ornithine to make polyamines and the amino acid proline, which is used to make collagen.

Ornithine can also elevate growth hormone levels in the body but only for a brief period of time. This doesn’t seem to notably affect overall health.

L-aspartic acid is a regulator of testosterone synthesis. It works in the central brain region to cause a release of hormones, such as luteinizing hormone, follicle-stimulating hormone, and growth hormone.

Besides this, L-aspartic acid has many additional functions in the body. It is necessary for removing toxins from the cells, proper immune function, producing ATP and glucose, improving memory and cognition, and more.

Possible benefits

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

Reduced fatigue – L-ornithine can reduce fatigue during prolonged cardiovascular exercise, hangovers, and hepatic pathology. All three situations are characterized by excessive ammonia concentrations in the blood.
Improved fertility – One study on infertile men found that 26.6% of subjects became fertile over 90 days of taking D-aspartic acid. In these men, sperm count and seminal mobility were increased by 50-100%, and luteinizing hormone was increased by 30-60%. This effect likely applies to L-aspartic acid as well but to a smaller extent.

Minor benefits

Reduced hangovers – Abnormally high ammonia levels are usually present during hangovers. Supplemental L-ornithine can rid the body of excess ammonia and lower the intensity of hangovers. Specifically, the amino acid can reduce fatigue and cortisol levels during a hangover, as well as improve sleep quality after drinking too much alcohol.
Increased testosterone levels – D-aspartic acid (and probably L-aspartic acid as well) can improve testosterone levels by about 30-60%. This effect can be long-lasting in infertile men. However, testosterone levels usually go back to baseline after 6-12 days of supplementation in men with normal fertility and testosterone levels. In healthy men who do resistance training, aspartic acid can decrease the amount of free and total testosterone.

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.

Nausea
Diarrhea
Increased cholesterol levels
Reduced testosterone – While the supplement can increase testosterone levels in infertile men, in healthy men who do resistance training, L-aspartic acid can actually decrease the amount of free and total testosterone.
Amino acid imbalance – Essential and non-essential amino acids should be kept in balance as they act synergistically in many ways. Too much of one amino acid can sometimes cause side effects if there isn’t enough of another amino acid. For example, this principle applies to glycine and methionine, lysine and arginine, and the BCAA trio. There are many other proven and unproven examples. Food or a protein powder is usually a better choice for getting enough amino acids unless you have a specific goal in mind targeted by a particular amino acid/s.
Toxicity – While acute toxicity is extremely rare, taking high amounts of either aspartic acid or ornithine could lead to chronic toxicity and cause some health problems. To prevent chronic toxicity, it is best to stay below 6 grams of ornithine and 3 grams of L-aspartic acid 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-ornithine-L-aspartate?

You should probably avoid taking the supplement if you:

get enough aspartic acid and ornithine from food or produce enough in the body
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:

produce too much ammonia (due to prolonged cardiovascular exercise or some liver conditions)
consume very little protein (less than 0.3 grams/pound of body weight)
are infertile or wish to improve fertility
have low total testosterone

How much L-ornithine-L-aspartate should you take?

Since both ornithine and aspartic acid can be found in food or synthesized in the body, you may already get sufficient amounts without taking them as a supplement. About 0.36 grams of protein/pound of body weight should generally be enough to prevent any symptom deficiency.

If you plan to take L-ornithine-L-aspartate as a supplement, 3-6 grams appears to be the best daily dose for most people. This amount should provide most of the benefits without meaningful side effects.

Some people may benefit from doses higher than 6 grams. These include people with excess ammonia due to prolonged cardiovascular exercise, certain liver diseases, and excess alcohol consumption.

The upper safety limit for L-ornithine-L-aspartate is not well-established. To stay on the safe side, don’t take more than 6 grams daily unless you have a great reason to do so. Higher amounts may cause problems if you take the supplement for a prolonged period.

Food sources of aspartic acid

Aspartic acid is found in all whole foods that contain dietary protein.

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

The easiest way to find out exactly how much aspartic acid 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.

Food sources of ornithine

Food rarely provides enough L-ornithine but it can be produced in the body from L-arginine and L-citrulline.

L-arginine is found in all whole foods that contain dietary protein. About 0.36 grams of protein per pound of body weight should be enough for most people to avoid any sign of deficiency.

The richest food source of citrulline is watermelon (2.1 mg/gram of wet weight). For raising L-arginine levels in the body, 330 grams of watermelon is equivalent to 1 gram of supplemental L-arginine.

Muskmelons, bitter melons, squashes, gourds, cucumbers, and pumpkins also contain high amounts of citrulline.

Best time to take L-ornithine-L-aspartate

Both ornithine and aspartic acid are water-soluble, so you don’t have to take them with food to absorb them well. To maximize absorption, take the supplement at least an hour before or after a meal so it doesn’t compete for absorption with other amino acids.

To maximize the benefits, take L-ornithine-L-aspartate right before a workout.

Whether you take the supplement in the morning or the evening doesn’t matter much. 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 won’t break your fast.

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

Interactions

L-arginine
Arginine promotes the uptake of ornithine into cells.
Other amino acids
Essential and non-essential amino acids should be kept in balance as they act synergistically in many ways. Too much of one amino acid can sometimes cause side effects if there isn’t enough of another amino acid. For example, this principle applies to glycine and methionine, lysine and arginine, and the BCAA trio. There are many other proven and unproven examples. Food or a protein powder is usually a better choice for getting enough amino acids unless you have a specific goal in mind targeted by a particular amino acid/s.
Alcohol
Alcohol can cause a quick rise in ammonia concentrations in the blood. Ornithine plays a major role in the urea cycle and helps convert ammonia into urea, helping to flush this toxic chemical out of the system. Supplemental L-ornithine has been shown to improve sleep quality after heavy drinking and reduce the intensity of hangovers.

Where to buy L-ornithine-L-aspartate

Amazon is the best option for ordering L-ornithine-L-aspartate 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 ornithine and aspartate, 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 of both L-ornithine and L-aspartic acid in the system can cause some health problems. It is best to stay below 6 grams a day to prevent these side effects.

You may need more of this amino acid if you:
– produce too much ammonia (due to prolonged cardiovascular exercise or some liver conditions)
– eat very little protein (less than 0.3 grams/pound of body weight)

You may need more of this amino acid if you:
– are infertile or wish to improve fertility
– have low total testosterone
– eat very little protein (less than 0.3 grams/pound of body weight)

You should notice the benefits within a week of supplementation. The increases in testosterone usually vanish in healthy adults after 6-12 days but can persist in infertile men or people with low testosterone.

You can easily find vegan-friendly L-ornithine-L-aspartate pills and 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, L-ornithine-L-aspartate is water-soluble, so you don’t have to take it with food to absorb it well.

L-ornithine-L-aspartate should not break a fast unless you take a very high dose at once. If you practice time-restricted eating, take this supplemenet 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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