Does L-theanine (L-theanine) cause gastrointestinal irritation?

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Last updated: March 3, 2025 • View editorial policy

From the Research

L-theanine is generally well-tolerated and does not cause significant gastrointestinal irritation in most people, as evidenced by the most recent and highest quality study available 1.

Key Points to Consider

  • L-theanine is an amino acid found in tea leaves, particularly green tea, and is available as a supplement in doses of 100-200 mg per day.
  • Unlike some supplements or medications, l-theanine does not increase stomach acid production or irritate the stomach lining, as suggested by studies on its metabolism and health effects 2, 3.
  • Most people can take l-theanine on an empty stomach without issues, though some individuals might experience mild digestive symptoms, and taking it with food may help alleviate these symptoms.
  • L-theanine works by influencing brain neurotransmitters and promoting relaxation without sedation, which is why it's often used for anxiety and stress relief, and these mechanisms don't directly impact digestive function 1.
  • If stomach discomfort occurs, reducing the dose or discontinuing use would be appropriate, and it's essential to consider individual tolerance and sensitivity when using l-theanine supplements.

Mechanisms and Effects

  • L-theanine may have a dose-dependent effect on gastric ulcer healing, as shown in a study where a low dose of 10 mg/kg body weight healed gastric ulcers, while a higher dose of 40 mg/kg body weight aggravated the condition 4.
  • The absorption and metabolism of l-theanine have been studied, and it is rapidly absorbed and seems to be hydrolyzed to ethylamine and glutamic acid, with a minor part retained in erythrocytes 3.
  • L-theanine administration may modulate the absorption of dietary nutrients and expression of transporters and receptors in the intestinal mucosa of rats, indicating potential effects on nutrient uptake and utilization 5.

Recommendations

  • Based on the current evidence, l-theanine can be considered safe for most people, and gastrointestinal irritation is unlikely to occur at typical supplement doses 1.
  • However, individual tolerance and sensitivity should be considered, and stomach discomfort should be monitored and addressed if it occurs.
  • Further research is needed to fully understand the effects of l-theanine on digestive function and overall health, but current evidence suggests it is generally well-tolerated and may have potential benefits for relaxation and cognitive function.

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.