Does Threonine Make You Sleepy? A Scientific Look at an Essential Amino Acid

December 24, 2025 •

5 min read

A 2019 study published in the journal eLife uncovered that dietary threonine promoted sleep and facilitated sleep onset in animal models, linking its metabolism to the brain's GABAergic system. This research brings new attention to the question: does threonine make you sleepy, and how might this essential amino acid influence our rest?

Quick Summary

Threonine's effect on sleep is under investigation, with animal studies showing it promotes sleep by modulating GABA-related pathways in the brain. The amino acid is a precursor to calming neurotransmitters like glycine and serine, but human-specific data on its sedative effects remains limited.

Key Points

Indirect Sleep Promotion: Threonine doesn't act as a direct sedative but may indirectly promote sleep by serving as a precursor to the calming neurotransmitters glycine and serine.
GABA Pathway Modulation: Animal studies have shown that dietary threonine can modulate GABA-related pathways in the brain, increasing total sleep duration and reducing the time it takes to fall asleep.
Limited Human Evidence: Most compelling evidence comes from animal research; specific, direct sedative effects in humans from standard threonine supplementation are not widely documented.
Supports Overall Health: Beyond direct neurochemical effects, threonine supports gut health, immune function, and liver health, all of which contribute to a body's ability to achieve restful sleep.
Differs from L-Theanine: Threonine is metabolically different from L-theanine, the amino acid found in tea. L-theanine promotes relaxation and mental clarity by increasing alpha brain waves, a distinct mechanism from threonine.
Dietary Intake is Best: As an essential amino acid, the best source of threonine is from high-protein foods like meat, dairy, and legumes, ensuring sufficient intake through a balanced diet.
Potential Side Effects: Supplemental threonine can cause minor side effects like stomach upset, headache, or nausea at high doses. Individuals with certain pre-existing conditions should consult a doctor before supplementing.

The Connection Between Threonine and Neurotransmitters

Threonine is an essential amino acid, meaning the body cannot produce it and must obtain it from diet. While known for its roles in protein synthesis, collagen formation, and immune function, its effect on the central nervous system has recently garnered interest. The primary mechanism linking threonine to sleepiness appears to involve its relationship with key neurotransmitters, particularly GABA and glycine.

GABA (gamma-aminobutyric acid) is the main inhibitory neurotransmitter in the brain, working to block or inhibit certain brain signals and reduce activity in the nervous system. The result is a calming and relaxing effect that promotes sleep. Early research, particularly a prominent 2019 study in fruit flies (Drosophila), found that increased dietary threonine led to higher sleep amounts and faster sleep onset. This was attributed to threonine's ability to modulate GABA levels and weaken GABA responses in specific brain neurons, thereby enhancing the drive for sleep.

Furthermore, threonine is a direct precursor to glycine, another amino acid with inhibitory effects in the central nervous system. Glycine is known for its calming properties and its ability to promote better sleep quality in humans, working through similar inhibitory pathways. By supporting the production of these calming neurotransmitters, threonine may indirectly contribute to a sense of drowsiness or improved rest.

Scientific Evidence from Animal Studies vs. Human Experience

The most compelling evidence for threonine's sedative effects comes from animal models, specifically the fruit fly study mentioned previously. In this research, scientists were able to precisely observe and manipulate the neurobiological pathways showing that threonine metabolism directly influences sleep drive. While these results are promising and offer a strong biological basis for a sleep-promoting effect, they are not a direct translation to humans. Research in humans is sparse, and many people do not report significant sleepiness from threonine supplementation. The effects may be subtle or highly individual, and influenced by a person's overall diet, metabolism, and existing health conditions.

It is also important to differentiate between threonine and the more commonly known L-theanine, which is derived from tea leaves and is often taken for relaxation. L-theanine has more established research in humans for promoting alpha brain waves associated with a relaxed but alert state, and may aid sleep without causing direct drowsiness. Threonine's mechanism is different, centered on neurotransmitter precursors rather than direct receptor modulation. This distinction is crucial for consumers to understand when seeking supplements.

Dietary Sources and Supplement Considerations

Since threonine is an essential amino acid, the best way to get it is through a balanced diet. High-protein foods are excellent sources of threonine, as it is a fundamental building block of proteins.

Animal Sources: Lean meats (chicken, turkey, beef), dairy products (cottage cheese, milk), and eggs are rich in threonine.
Plant-Based Sources: Legumes (beans, lentils), whole grains (quinoa, wheat), and some nuts also provide a good amount of threonine.

For those considering supplementation, it's vital to consult a healthcare provider. While generally considered safe in doses of up to 4 grams daily for adults, higher doses can lead to side effects like upset stomach, nausea, or headache. People with Amyotrophic Lateral Sclerosis (ALS) or taking certain Alzheimer's medications should be cautious and discuss risks with a doctor.

Potential Sleep Mechanisms: A Comparison

To better understand how threonine might affect sleep, here's a comparison of its potential mechanisms versus more established sleep aids.


Mechanism	Threonine	L-Theanine	Tryptophan	Melatonin
Primary Function	Precursor to calming neurotransmitters (glycine, serine). Influences GABAergic system.	Increases GABA, serotonin, and dopamine; promotes relaxing alpha brain waves.	Precursor to serotonin and melatonin, the body's sleep hormone.	Directly regulates the body's circadian rhythm.
Effect on Sleep	May indirectly promote sleep by supporting calming neurotransmitter production. Limited human evidence.	Reduces anxiety and promotes relaxation, aiding restful sleep without inducing direct drowsiness.	A well-known aid that helps the body produce sleep-inducing chemicals.	A hormone that signals the body it's time to sleep.
How It Works	Influences neurotransmitter pathways indirectly through metabolism, as shown in animal studies.	Crosses the blood-brain barrier to modulate neurotransmitter levels and brainwave activity directly.	Is converted into 5-HTP, which then becomes serotonin and subsequently melatonin.	Is produced by the pineal gland and signals the body to prepare for sleep.
Primary Research	Animal models (fruit flies), showing dose-dependent effects on sleep.	Extensive research in humans showing anxiety reduction and improved sleep quality.	Decades of research linking it to sleep pathways.	Well-established human research demonstrating efficacy for circadian rhythm disorders.

How Threonine Supports Other Sleep-Related Functions

Beyond its potential direct influence on neurotransmitters, threonine plays several other roles that contribute to overall health, which can in turn support better sleep.

Supports Gut Health and Immunity

Threonine is a key component of mucin, a protein that forms the protective mucus layer of the digestive tract. A healthy gut lining is crucial for overall health and can influence immune function and even mood, both of which are closely tied to sleep. Threonine deficiency can impact the integrity of this mucosal barrier and impair immune function, potentially disrupting sleep patterns indirectly.

Aides Liver Function

Threonine is involved in fat metabolism in the liver and helps prevent fatty liver disease. Liver health is an important component of detoxification and overall metabolic balance, and a properly functioning liver can contribute to better sleep quality.

Conclusion

So, does threonine make you sleepy? The existing scientific evidence, primarily from animal studies, suggests that threonine has the potential to influence sleep-promoting neurotransmitter systems like GABA and glycine, and may increase the drive for sleep. While it is not a traditional sedative and human data is limited, its role as a precursor to calming brain chemicals offers a compelling explanation for its sleep-related effects. Most people will likely not feel a strong sense of drowsiness from dietary threonine alone. However, for those seeking to naturally support their body's sleep mechanisms, understanding threonine's indirect influence can be valuable. As always, consulting a healthcare professional before starting any new supplement regimen is recommended to ensure it's the right choice for your individual health needs.

Visit the National Institutes of Health website for more information on amino acid metabolism and neuroscience research.

Frequently Asked Questions

While threonine may support sleep, it is not a direct treatment for insomnia. The evidence for its sleep-promoting effects comes largely from animal studies and its function as a precursor to calming neurotransmitters. For persistent insomnia, it is best to consult a healthcare provider for a comprehensive treatment plan.

Threonine is an essential amino acid that supports calming neurotransmitter production and protein synthesis. L-theanine, often found in tea, promotes relaxation and calmness by increasing alpha brain waves, a different mechanism altogether.

Threonine is generally well-tolerated in doses up to 4 grams daily. However, some people may experience side effects such as stomach upset, headache, nausea, and skin rash.

Threonine can be metabolized into glycine and serine, two amino acids that function as inhibitory neurotransmitters in the central nervous system, which helps promote a calming effect. Animal studies also show it can modulate GABAergic signaling.

You can find threonine in high-protein foods like meat, dairy, and eggs. Plant-based sources include legumes such as beans and lentils, as well as whole grains.

It is crucial to consult a healthcare provider before combining threonine with any medication. For instance, threonine may interact with NMDA antagonists, a class of drugs used for Alzheimer's disease.

Animal studies, like those on fruit flies, offer insights into the biological mechanisms of threonine's effect on sleep. While promising, these findings do not directly translate to human effects, and more research is needed to determine the exact impact on human sleep.