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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Amino Acid [EPC]
Leucine is an essential branched-chain amino acid (BCAA) and a primary regulator of muscle protein synthesis via the mTOR pathway. It is used clinically in parenteral nutrition and as a dietary supplement to support nitrogen balance and muscle health.
Name
Leucine
Raw Name
LEUCINE
Category
Amino Acid [EPC]
Drug Count
24
Variant Count
68
Last Verified
February 17, 2026
RxCUI
800401, 800405, 800416, 800420, 800434, 800438, 800440, 800444, 801644, 801648, 800341, 800345, 800188, 800192, 800237, 800241, 800998, 801000, 801010, 801012, 801019, 801021, 801029, 801031, 1090635, 1090639, 831426, 831430, 800584, 800588, 801133, 801136, 1601982, 800611, 1189640, 801395, 801398, 801403, 801405
UNII
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About Leucine
Leucine is an essential branched-chain amino acid (BCAA) and a primary regulator of muscle protein synthesis via the mTOR pathway. It is used clinically in parenteral nutrition and as a dietary supplement to support nitrogen balance and muscle health.
Detailed information about Leucine
This page is for informational purposes only and does not replace medical advice. Consult a qualified healthcare professional before using any medication containing Leucine.
Leucine (L-leucine) is a proteogenic, branched-chain essential amino acid (BCAA) that plays a critical role in human metabolism, specifically in the regulation of protein synthesis and glucose homeostasis. As an 'essential' amino acid, the human body cannot synthesize leucine de novo (from scratch); therefore, it must be acquired through dietary intake or supplementation. Leucine belongs to the pharmacological class known as Amino Acids [EPC]. In clinical settings, leucine is a fundamental component of Total Parenteral Nutrition (TPN) and various enteral nutritional formulas designed to maintain nitrogen balance and prevent muscle wasting in critically ill patients.
Historically, the FDA has recognized leucine as a 'Generally Recognized as Safe' (GRAS) substance for use as a nutrient and dietary supplement. Beyond its role as a building block for proteins, leucine acts as a potent signaling molecule. It is uniquely capable of stimulating the mammalian target of rapamycin (mTOR) complex, which is the primary regulatory pathway for cell growth and protein translation. This makes leucine a subject of intense clinical interest for conditions ranging from sarcopenia (age-related muscle loss) to metabolic disorders.
Your healthcare provider may prescribe or recommend leucine-containing products as part of a broader nutritional strategy, particularly if you are recovering from surgery, trauma, or managing a chronic wasting disease. It is important to distinguish between the various forms of leucine, including L-leucine (the naturally occurring form) and its metabolites like beta-hydroxy beta-methylbutyrate (HMB), though this guide focuses primarily on the parent amino acid.
Leucine operates through several sophisticated molecular mechanisms that distinguish it from other amino acids. At the cellular level, leucine serves as a primary activator of the mTORC1 (mammalian target of rapamycin complex 1) signaling pathway. This occurs through its interaction with the Sestrin2 protein, which acts as a leucine sensor. When leucine levels are sufficient, it triggers a cascade that leads to the phosphorylation of p70S6 kinase and the inhibition of 4E-BP1 (eukaryotic initiation factor 4E-binding protein 1), both of which are essential for initiating the translation of mRNA into new muscle proteins.
Furthermore, leucine influences glucose metabolism by stimulating the secretion of insulin from the pancreatic beta cells. It acts as an allosteric activator of glutamate dehydrogenase, increasing the oxidation of glutamate and providing the ATP necessary for insulin release. This dual action—promoting protein synthesis while modulating insulin—makes leucine a critical regulator of the body's anabolic (building) state.
In the context of the nervous system, leucine competes with other large neutral amino acids (LNAAs) like tryptophan and tyrosine for transport across the blood-brain barrier via the LAT1 (Large Neutral Amino Acid Transporter 1). This competition can influence the synthesis of neurotransmitters such as serotonin and dopamine, which is why excessive or imbalanced leucine intake must be carefully monitored by a healthcare professional.
Leucine is FDA-approved as a component of parenteral and enteral nutrition products for patients requiring nutritional support due to an inability to ingest, digest, or absorb nutrients via the oral route. Key indications include:
Leucine is available in several formulations, often in combination with other amino acids:
> Important: Only your healthcare provider can determine if Leucine is right for your specific condition. Clinical use, especially in IV form, requires strict medical supervision.
Dosage for leucine varies significantly based on the clinical indication and the patient's overall nutritional status.
Leucine is essential for pediatric growth, but requirements are highly age-dependent.
Note: In children with Maple Syrup Urine Disease (MSUD), leucine intake is strictly limited and must be managed by a metabolic specialist.
In patients with chronic kidney disease (CKD), nitrogenous waste products can accumulate. While leucine is an essential amino acid, total protein intake (including leucine) may need to be restricted in non-dialysis patients to 0.6-0.8 g/kg/day. Patients on hemodialysis may require higher doses due to amino acid loss during the dialysis procedure.
Patients with hepatic encephalopathy or advanced cirrhosis may have altered BCAA-to-AAA (aromatic amino acid) ratios. Healthcare providers may specifically increase the ratio of leucine and other BCAAs in these patients to help reduce ammonia levels and improve neurological function.
Older adults often exhibit 'anabolic resistance,' meaning they require higher concentrations of leucine (approx. 3-4 grams per meal) to trigger the same muscle protein synthesis response as younger individuals.
If you miss a dose of an oral leucine supplement, take it as soon as you remember. If it is almost time for your next scheduled dose, skip the missed dose and resume your regular schedule. Do not double the dose to catch up. For patients on IV nutrition, the infusion rate is managed by healthcare professionals; do not attempt to adjust the pump settings yourself.
Acute overdose of leucine is rare but can lead to metabolic disturbances. Symptoms of excessive intake (hyperleucinemia) may include:
In the event of a suspected overdose, contact your local poison control center or seek emergency medical attention immediately. Treatment is generally supportive, focusing on hydration and blood glucose management.
> Important: Follow your healthcare provider's dosing instructions. Do not adjust your dose without medical guidance.
While leucine is generally well-tolerated when consumed within recommended ranges, high oral doses can cause gastrointestinal distress. Common symptoms include:
These effects are usually transient and subside as the body adjusts to the supplement or when the dose is reduced.
> Warning: Stop taking Leucine and call your doctor immediately if you experience any of these serious symptoms:
Prolonged intake of very high doses of leucine (exceeding 30-50 grams per day) may lead to several chronic issues:
There are currently no FDA black box warnings for Leucine. It is considered a safe nutritional component when used according to established guidelines. However, it is contraindicated in patients with Maple Syrup Urine Disease (MSUD), a condition that would be identified in neonatal screening.
Report any unusual symptoms to your healthcare provider. Monitoring of blood amino acid profiles may be necessary for those on long-term, high-dose therapeutic regimens.
Leucine is a potent metabolic regulator and should not be viewed merely as an inert food additive. Patients must ensure they are maintaining a balanced intake of all three branched-chain amino acids (BCAAs). Taking leucine in isolation over long periods can lead to a depletion of plasma levels of valine and isoleucine, which may impair muscle growth and cause metabolic imbalances. Always inform your healthcare provider about all supplements you are taking, especially if you have a history of metabolic or endocrine disorders.
No FDA black box warnings for Leucine. Leucine is an essential nutrient required for human life; however, its pharmacological use in concentrated forms requires adherence to safety guidelines to avoid metabolic disturbances.
If you are taking therapeutic doses of leucine or receiving it via IV, your healthcare provider may monitor:
Leucine generally does not cause sedation or cognitive impairment. However, if you experience dizziness or shakiness due to its effects on blood sugar, you should avoid driving or operating heavy machinery until you know how the supplement affects you.
Alcohol can interfere with protein synthesis and may exacerbate the gastrointestinal side effects of leucine. Furthermore, chronic alcohol consumption can deplete B-vitamins, which are necessary for leucine metabolism. It is generally advised to limit alcohol intake when using leucine for therapeutic muscle recovery.
There is no known withdrawal syndrome associated with stopping leucine. However, if you are using it to manage a specific medical condition like sarcopenia or a urea cycle disorder, stopping the supplement abruptly may lead to a return of symptoms or a decline in nitrogen balance. Always consult your doctor before discontinuing a prescribed nutritional regimen.
> Important: Discuss all your medical conditions with your healthcare provider before starting Leucine.
There are few absolute contraindications for leucine; however, it must NEVER be used in patients with Maple Syrup Urine Disease (MSUD). In this population, the inability to metabolize leucine leads to the accumulation of alpha-ketoisocaproate, which causes severe cerebral edema, neurological damage, and death. No medication should be used to 'offset' this risk; total avoidance of supplemental leucine is mandatory.
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking.
Leucine must NEVER be used in the following circumstances:
Conditions requiring careful risk-benefit analysis by a physician:
There is no established cross-sensitivity between leucine and other drug classes. However, patients who are allergic to specific protein sources (such as whey, soy, or eggs) should ensure their leucine supplement is not derived from those sources. Synthetic or fermentation-derived L-leucine is typically preferred for patients with severe food allergies.
> Important: Your healthcare provider will evaluate your complete medical history before prescribing Leucine.
Leucine is a naturally occurring essential amino acid and is a normal component of the human diet. During pregnancy, the demand for amino acids increases to support fetal growth and placental development. However, the safety of high-dose leucine supplementation (above dietary levels) has not been established in pregnant women.
Leucine is a natural component of breast milk and is essential for the nursing infant's development. Supplemental leucine taken by the mother will increase the leucine content of the milk. While this is generally safe, excessive doses could theoretically disrupt the amino acid balance of the milk. Nursing mothers should consult their healthcare provider before starting high-dose BCAA supplements.
Leucine is vital for pediatric growth and is a standard component of infant formulas and pediatric TPN.
Leucine is increasingly studied in the elderly for the treatment of sarcopenia.
In patients with kidney disease, the kidneys' ability to excrete urea (the byproduct of leucine metabolism) is diminished.
In patients with liver cirrhosis, the liver's ability to process aromatic amino acids (AAA) is impaired, while BCAA metabolism (which occurs in the muscle) remains relatively intact.
> Important: Special populations require individualized medical assessment.
Leucine's primary mechanism of action is the nutrient-sensing activation of the mTORC1 pathway. Unlike other amino acids, leucine acts as a direct signal to the cell that sufficient energy and building blocks are available for protein synthesis. It binds to the protein Sestrin2, which then releases its inhibition of the GATOR2 complex. This triggers a series of events involving Rag GTPases that recruit mTORC1 to the lysosomal surface, where it becomes activated. Once active, mTORC1 phosphorylates 4E-BP1 and S6K1, leading to increased ribosomal biogenesis and the initiation of protein translation.
Additionally, leucine acts as a secretagogue for insulin. It serves as a substrate for the enzyme glutamate dehydrogenase (GDH) in pancreatic beta cells, increasing the ATP/ADP ratio and triggering the release of insulin, which further enhances the anabolic environment.
| Parameter | Value |
|---|---|
| Bioavailability | >90% (Oral) |
| Protein Binding | Negligible |
| Half-life | 1 - 2 hours |
| Tmax | 0.5 - 1 hour |
| Metabolism | Primarily Skeletal Muscle (BCAT/BCKDH enzymes) |
| Excretion | Renal (as Urea) and Respiratory (as CO2) |
Leucine is classified as an Essential Amino Acid and is part of the Branched-Chain Amino Acid (BCAA) group. It is categorized under Amino Acids [EPC] in the FDA's Established Pharmacologic Class system. It is related to Isoleucine and Valine but is the only purely ketogenic member of the group.
Medications containing this ingredient
Common questions about Leucine
Leucine is primarily used to stimulate muscle protein synthesis and maintain nitrogen balance in the body. Clinically, it is a vital component of intravenous nutrition for patients who cannot eat and is used in specialized diets for those with muscle-wasting conditions. Many individuals also use it as a dietary supplement to support recovery from exercise and to prevent age-related muscle loss. It works by activating the mTOR signaling pathway, which tells the body to begin building new proteins. Always consult a healthcare provider before using it for therapeutic purposes.
When taken in standard doses, the most common side effects of leucine are gastrointestinal in nature, including nausea, stomach cramps, bloating, and diarrhea. These symptoms usually occur when high doses of powder are taken on an empty stomach or without sufficient water. Some people may also experience mild headaches or a temporary change in appetite. Most of these effects are mild and resolve quickly once the supplement is stopped or the dosage is reduced. If you experience severe abdominal pain or persistent vomiting, you should contact your doctor.
It is generally recommended to limit alcohol consumption while taking leucine, especially if you are using it to build muscle or recover from an injury. Alcohol can significantly impair the body's ability to synthesize new proteins, effectively neutralizing the benefits of leucine. Additionally, alcohol can worsen the stomach upset that some people experience with leucine supplements. Chronic alcohol use also depletes B-vitamins, which are necessary for the body to process leucine correctly. Speak with your healthcare provider about what level of alcohol consumption is safe for your specific health status.
Leucine is an essential amino acid that is naturally present in protein-rich foods and is necessary for a healthy pregnancy. However, the safety of taking concentrated leucine supplements during pregnancy has not been extensively studied in clinical trials. Most doctors recommend that pregnant women meet their leucine needs through a balanced diet containing meat, dairy, or legumes rather than through high-dose supplements. If you are pregnant or planning to become pregnant, discuss your nutritional needs with your obstetrician before starting any BCAA or amino acid supplements. Excessive intake could potentially disrupt the balance of other essential amino acids.
The molecular effects of leucine happen very quickly, with plasma levels peaking within 30 to 60 minutes after oral ingestion. The stimulation of muscle protein synthesis typically begins within an hour and reaches its peak around 90 to 120 minutes after taking the supplement. However, visible results in terms of muscle growth or improved recovery usually take several weeks of consistent use combined with proper nutrition and exercise. For patients receiving leucine via IV for medical reasons, the metabolic benefits are monitored through blood tests and nitrogen balance studies over several days. Consistency and timing are key to seeing the benefits of leucine.
For most healthy individuals using leucine as a dietary supplement, there is no danger in stopping it suddenly, as it does not cause physical dependence or withdrawal symptoms. However, if you have been using it to manage a specific medical condition like sarcopenia or as part of a medically supervised nutrition plan, stopping abruptly may result in a decline in muscle mass or a return to a negative nitrogen balance. It is always best to discuss any changes to your supplement routine with your healthcare provider. They can help you determine if you still need the supplement or if you can meet your needs through diet alone.
If you miss a dose of an oral leucine supplement, you should take it as soon as you remember. However, if it is nearly time for your next scheduled dose, it is better to skip the missed dose and continue with your regular routine. You should never take a double dose to make up for a missed one, as this increases the risk of stomach upset and metabolic imbalance. For those receiving leucine through a medically managed IV or feeding tube, the schedule is controlled by healthcare professionals, and any interruptions should be reported to the nursing staff immediately. Regularity is important for maintaining the 'leucine trigger' for protein synthesis.
Leucine itself is very low in calories and does not directly cause an increase in body fat. Instead, it is used to promote the growth of lean muscle mass, which may lead to an increase in weight on the scale even as body composition improves. Because muscle is denser than fat, you may find that your weight increases slightly while your body becomes firmer and more toned. However, if leucine is taken as part of a high-calorie protein shake or supplement, the total calories in those products could lead to fat gain if not balanced with activity. Your healthcare provider can help you integrate leucine into a weight management plan.
Leucine can interact with several types of medications, so it is important to be cautious. The most significant interactions occur with diabetes medications (like insulin) and Parkinson's disease medications (like Levodopa). Because leucine can lower blood sugar, taking it with diabetes drugs may increase the risk of hypoglycemia. It also competes with Levodopa for entry into the brain, which can make the medication less effective. Always provide your doctor with a full list of all medications and supplements you are taking to ensure there are no dangerous interactions. They may suggest timing your doses differently to avoid these problems.
Yes, leucine is widely available as a generic dietary supplement and as a component in many generic intravenous amino acid solutions. Because it is a naturally occurring amino acid rather than a synthetic drug, it is produced by many different manufacturers and is generally very affordable. You can find it in various forms, including pure L-leucine powder, capsules, and as part of BCAA (branched-chain amino acid) blends. When purchasing a generic supplement, look for products that are third-party tested (such as by USP or NSF) to ensure purity and accurate labeling. Your pharmacist can recommend a high-quality version that meets your needs.