L-Theanine is a non-essential amino acid derived from the Camellia sinensis plant species. It was first discovered circa 1950 in which it was noted within the contents of green tea; it serves as a “building block” for proteins and is also present in other types of tea (e.g. black tea). For generations L-theanine has been utilized as a natural supplement to treat anxiety and stress, and has been investigated as a cognitive enhancer (nootropic) when administered synergistically with caffeine.
In addition to alleviating stress and enhancing cognition, preliminary research suggests additional L-theanine benefits including: anticancer properties, neuroprotective effects, sleep enhancement, and adjunctive efficacy as a treatment for schizophrenia. In terms of structure, L-theanine closely resembles the neurotransmitter glutamate, and thus is capable of binding to glutamate receptors to a modest extent; serving as an antagonist at the AMPA and kainate receptor sites. Further, L-theanine acts as an NMDA receptor agonist to a minor extent, while simultaneously inhibiting reuptake of glutamate and glutamine.
The substance is known to alter levels of various other neurotransmitters including: GABA, dopamine, and serotonin – plus alter neurotrophins such as BDNF and NGF. Despite its highly complex, multi-faceted mechanism of action, L-theanine isn’t commonly associated with side effects. In fact, most scientific literature suggests that even when administered at supratherapeutic levels, no significant side effects or adverse reactions are apparent.
Factors that influence L-Theanine side effects
Despite the fact that no significant side effects from L-theanine administration have been reported in scientific literature does not mean that they don’t exist. Some people can still experience side effects and/or adverse reactions with this supplement. There are several factors to consider that may influence the severity and/or number of side effects that you experience.
1. Dosage (200 mg to 1,200 mg)
As with most drugs and supplements, the greater the dosage, the greater the neurophysiological backlash you’ll experience. Anytime you introduce a new stimuli to your body, whether it be a supplement like L-theanine or hard drug, the dosage usually dictates the severity and quantity of side effects. Generally those at the higher end of the dosing spectrum will get a greater effect compared to those at the lower end of the spectrum.
Someone taking 200 mg of L-theanine is unlikely to experience any significant side effect, yet someone taking over 1,200 mg will be more likely to notice side effects. Sometimes the ratio of dose to bodyweight is an influential factor. Just like some bigger individuals can tolerate copious amounts of alcohol, smaller statured individuals may not be able to handle as large of a dose.
While the concept of dose in relation to bodyweight is always used in mice and rodent studies, it is seldom advised for humans – despite the fact that it is a proven paradigm. To minimize the likelihood of side effects from L-theanine supplementation, you’ll want to take the minimal effective dose. In other words, strive to take the amount that gives you therapeutic benefit, yet yields few (or no) side effects.
2. Individual variation
Another important factor to consider when experiencing side effects is individual variation. Why do some people experience side effects from L-theanine, yet others only notice benefit? It is important to consider the influence of genetics, lifestyle, environment, stressors, neurophysiology, and arousal when considering the side effects a person experiences.
Two people could be administered the same dose of L-theanine, yet one person may feel increasingly groggy or feel cognitively impaired – while the other feels more relaxed and alert. The difference between these two individuals could be related to certain genetic biomarkers that interact with the supplement or other stressors. Although certain drug reactions can be predicted in advance with technologies like GeneSight – this doesn’t yet apply to supplements.
In addition, your unique neurochemistry (neurotransmitters, brain waves, brain structure, regional activation) will all dictate your response to L-theanine. Some people will report favorable, noticeable responses – yet others may experience side effects. Due to the fact that L-theanine isn’t associated with many side effects, individual variation may be a strong influential factor.
This ties in with the variable of individual variation, but it is necessary to consider potential interactions between L-theanine and other drugs (or supplements). If you’re a heavy drinker of alcohol and supplement with L-theanine, it is important to consider the fact that these substances could interact. Individuals that are taking pharmaceutical drugs, ingesting illicit drugs, or even taking other supplements may experience side effects stemming from interactions.
It is important to consider the contraindications associated with L-theanine and other substances prior to supplementation. Many speculate that L-theanine may interact most strongly with CNS depressants such as alcohol and especially anxiolytic sedatives (e.g. benzodiazepines). Some evidence suggests that L-theanine elicits synergistic effects with these substances.
4. Time Span + Frequency
The duration over which you use L-theanine as a supplement may influence the side effects that you experience. Someone that has taken L-theanine for a few days may experience short-term effects as their body learns to adapt to the physiological changes being made by the substance. Others may not experience short-term effects, but may find that side effects emerge as they take L-theanine over a longer term.
In addition to time span (duration over which you’ve used L-theanine), it is important to consider the frequency of usage. Someone who administers L-theanine several times per day, on a daily basis may develop certain tolerances to the substance – eventually leading to them taking higher doses. As a person increases their dosage into the supratherapeutic range, the prevalence of side effects may increase.
To minimize the likelihood of side effects that you experience, consider taking L-theanine for short periods and cycling off. Limit the frequency of supplementation to an “as needed” basis to minimize likelihood of building tolerance, ultimately allowing you to maintain a low dose, which generally reduces potential side effects.
5. Specific Source (Brand)
While most L-theanine supplements are similar, being similar does not necessarily mean they are identical in composition. It is important to consider the brand and/or source of the L-theanine that you purchase. For example, some people purchase a specific “brand name” version of L-theanine called “Suntheanine” which contains a specific percentage of the “L” levorotatory enantiomer compared to the “D” dextrorotatory enantiomer.
Other sources may market their supplement as “L-theanine” but have more of a racemic mixture of the L-Theanine and D-theanine. In addition to the racemic composition, it is important to consider variation in quality between brands. Certain brands may manufacture L-theanine with varying amounts of herbal extracts or other trace elements.
Some supplement companies do a better job of manufacturing quality L-theanine than others, and many individuals will report subjective differences in “efficacy” between certain brands – which could be influenced by manufacturing quality. While the specific source of L-theanine is relatively minor, it should not be assumed that every batch is the “exact” same. This means that specific sources or brands may trigger more side effects than others for certain individuals.
L-Theanine Side Effects & Adverse Reactions (List)
Most medical professionals and researchers suggest that L-theanine supplementation isn’t associated with any significant side effects nor adverse reactions. In addition, the FDA considers L-theanine to be a GRAS (Generally Recognized As Safe) supplement. Despite the fact that there isn’t significant scientific evidence to suggest side effects from L-theanine doesn’t mean that they never occur.
Below are some of the more commonly reported side effects from L-theanine supplementation. Of the side effects on this list, the most common tend to include: dizziness, gastrointestinal discomfort, and headaches.
- Appetite changes: Some people have noted that when taking L-theanine, they experience appetite changes. For many individuals, these appetite changes will not be substantial, but may be noticeable. L-theanine within green tea and/or when combined with caffeine may aid in the suppression of appetite.
- Blood pressure reduction: There is some evidence to suggest that L-theanine can reduce hypertension and/or attenuate stress-induced blood pressure increases. It is unknown as to whether a blood pressure reduction may also occur among individuals with normal blood pressure. Individuals taking antihypertensive drugs or with lower blood pressure may want to be cognizant of this potential side effect.
- Brain fog: L-theanine as a standalone supplement is not a scientifically-proven cognitive enhancer. Certain studies have shown that it actually decreases cognitive performance on a variety of tasks when administered in isolation. If you find yourself getting brain fog from L-theanine, adding some caffeine to the equation should reverse this side effect.
- Brain wave alterations: It is scientifically proven that L-theanine alters brain waves, specifically increasing alpha waves. This effect is most noticeable among individuals who are stressed and/or anxious. Individuals with excess alpha activity and/or problems generating sufficient beta waves may perceive this as an unwanted side effect; for most people increased alpha should be considered beneficial.
- Cognitive slowing: When taken at high doses in isolation, L-theanine may impair various aspects of cognition, leading to slowed cognition. If you feel as if your cognitive function is impaired following administration of L-theanine, there’s a possibility that it has been. To prevent cognitive slowing from L-theanine and to enhance your cognitive function, take it with caffeine (or another stimulatory agent).
- Diarrhea: Some people experience diarrhea when they first start taking L-theanine. Diarrhea may be indicative of a poor quality brand of L-theanine or simply could be related to gastrointestinal distress. To reduce the likelihood of diarrhea, you have a number of options including: scale back on dosing, switch brands, take Imodium, discontinue, or tough it out and see if the diarrhea subsides.
- Dizziness: Among the most common side effects from L-theanine supplementation is dizziness. If you start taking this supplement and feel as if you’re too dizzy to function, feel semi-drugged, or even drunken – you may have taken too high of a dose. To minimize the likelihood of dizziness, start with a low dose and realize that the dizziness may subside as your physiology adapts to the L-theanine.
- Gastrointestinal discomfort: Another common side effect of L-theanine is gastrointestinal discomfort and/or pain. If you notice that your digestive system is acting up and/or you feel stomach pain, it could be from the supplementation. To minimize this side effect, you’ll want to consider taking it with food and/or at a lower dose.
- Headaches: Many people report headaches from L-theanine, which is relatively counterintuitive because the supplement increases relaxation. A majority of headaches associated with supplementation occur for a few days, and diminish as a person’s body adjusts to the effect of the supplement. The headaches stemming from L-theanine may be related to its complex effect on nitric oxide, which is known to cause headaches.
- Low energy: Taking L-theanine may promote increased physical and mental relaxation. While increased relaxation is nice, some individuals may note reduced overall energy as a result. If L-theanine is making you feel increasingly sluggish, you could augment its supplementation with caffeine and/or reduce the dosage. Understand that reductions in energy may be temporary and associated with neurophysiological adjustments to the supplement.
- Low serotonin: L-theanine has been suggested to alter neurotransmission of serotonin – some evidence suggesting increases, while other studies suggesting decreases. The evidence suggesting decreases note that while L-theanine increases levels of tryptophan (a precursor to serotonin), it reduces cortical levels of serotonin (5-HT) and decreases serotonin synthesis (5HIAA). Among certain individuals, a decrease in serotonin and/or serotonergic adjustment may serve as an unwanted side effect.
- Nausea: It is possible to feel nauseated following supplementation with L-theanine. This nausea may be more common when administered on an empty stomach, but may also be a sign that your body is not well-adapted to accommodating large doses. To minimize the likelihood of feeling nauseous, start with a low dose and titrate upwards.
- Sleepiness: While L-theanine doesn’t seem to cause drowsiness and/or somnolence in most individuals, it may synergistically exacerbate sleepiness among individuals that are already tired, fatigued, and/or taking a CNS depressant (e.g. alcohol). It is also important to consider that when taken at extremely high doses, its anxiolytic effect may be potent enough to provoke sleepiness in certain individuals.
- Stomach aches: It is very common to develop stomach aches following L-theanine supplementation. L-theanine is known to cause gastrointestinal distress and may provoke diarrhea. If you notice that you’re feeling stomach pain after taking L-theanine, you may want to consider taking it with food and/or reducing the dosage until your body adapts to its effect.
- Vomiting: In rare cases, nausea from L-theanine may become significant enough to provoke vomiting. Those that vomit from L-theanine are most likely to either have: taken too high of a dose, taken it on an empty stomach, purchased from a low quality brand, and/or taken it with another substance (spurring an interaction). If you’re certain that L-theanine is the culprit for your vomiting spell, discontinuation is advised.
- Weight loss: Preclinical evidence (from rodent studies) suggests that L-theanine may elicit anti-obesogenic effects. In other words, it could help reduce the likelihood of weight gain, and may even promote weight loss. While L-theanine isn’t often regarded as a weight loss drug, it is theoretically plausible that weight loss may result (in certain individuals) from supplementation.
Note: It is important to reemphasize that side effects are subject to significant individual variation. Also, it is necessary to understand that those who experience side effects from L-theanine are unlikely to experience every aforementioned possibility.
- Source: http://www.ncbi.nlm.nih.gov/pubmed/18006208
L-Theanine: Analyzing the Benefits (Pros) and Side Effects (Cons)
Anytime you’re taking a supplement like L-theanine, you should conduct a cost-benefit analysis to determine whether the therapeutic benefits (pros) outweigh the side effects (cons). Since this supplement isn’t associated with any clinically significant side effects, most people find that the benefits significantly outweigh the drawbacks. For example, someone with high anxiety and/or who experiences stress-induced cognitive impairment may derive significant benefit from L-theanine.
Even if this individual experiences a minor side effect such as slight nausea or an upset stomach, the therapeutic benefit outweighs these side effects. In other cases, it may be more difficult to determine whether the benefits outweigh the drawbacks. For example, if you’re taking L-theanine for anxiety, but find that it’s providing minimal benefit and making you feel really dizzy – it may be worth discontinuing.
In other scenarios, certain individuals may find no significant benefit and experience no significant side effects. In this case, it may be worth stopping L-theanine to save yourself the expense of buying supplements. It should be noted that individuals prone to anxiety and stress often derive more benefit from L-theanine than individuals who are naturally more laid back and less stressed; this has been noted in research.
Have you experienced L-Theanine side effects?
If you’ve supplemented with L-theanine, feel free to share whether you experienced any significant side effects in the comments section below. To help others understand your situation, document the dosage of L-theanine you had been taking, the specific brand, and how frequently you take it. In addition, note when the side effects emerged and/or if they ever subsided.
To those that experienced side effects, how can you be sure it was from the L-theanine? Were you only taking L-theanine or ingesting other drugs and supplements? Finally, include whether you believe the benefits associated with L-theanine supplementation were substantial enough to outweigh any side effects.