The trend of “stacking” supplements—combining them to amplify health benefits—has gained popularity in the wellness community. Some have suggested that combining GABA and L-theanine, two supplements marketed for managing stress and anxiety, may provide a stronger calming effect.

L-theanine, in doses between 200 and 400 mg per day, has shown promise in reducing stress and anxiety. Similarly, a few small studies have indicated that GABA-fortified oolong tea may help relieve stress. However, hard data on the benefits and effectiveness of taking these supplements together remain limited.

“There have been no human studies to provide guidance on the efficacy or dosage for ‘stacking’ L-theanine and GABA,” Ana Lupu, PharmD, ambulatory clinical pharmacist at UPMC Western Psychiatric Hospital, told Verywell in an email.

Animal research, such as a 2019 study in rats, found that a combination of GABA and L-theanine improved sleep. But whether this effect translates to humans — and whether it might help with anxiety — remains uncertain.

“Stress and sleep management are complex topics. Current evidence suggests that L-theanine may be a useful adjunct to the management of anxiety when combined with lifestyle changes. In contrast, the data supporting GABA for stress relief is less compelling; its use should primarily focus on facilitating sleep,” said Lupu.

Before you try GABA and L-theanine together, here’s what you should know.

Can taking GABA and L-theanine together reduce stress?

The human body naturally produces GABA, a chemical that blocks certain messages in the brain and calms the body, but studies have found mixed results for the use of GABA supplements.

“GABA is active in the central nervous system, but we’re not sure if much of this supplement will actually cross the blood-brain barrier and get into that central nervous system,” he said. Jamie Alan, RPh, PharmD, PhDassociate professor of pharmacology and toxicology at Michigan State University College of Human Medicine.

In other words, GABA supplements may not be effective if they cannot travel to the necessary areas of the body. Although more research is needed, current evidence provides limited support for the benefits of GABA supplements in reducing stress or improving sleep.

L-theanine, on the other hand, is an amino acid found in green tea and mushrooms that can cross the blood-brain barrier. Existing studies show that L-theanine can improve memory and attention.However, like most supplements, more research is needed to fully understand their impact on humans.

“There might be a benefit to trying L-theanine, but adding GABA on top of that, the benefit is unlikely,” added Alan.

Is it safe to stack L-theanine and GABA?

Studies have not identified serious side effects of GABA supplements, but taking more than 300 mg at a time may cause headaches, drowsiness, or abdominal discomfort. In addition, GABA supplements may lower blood pressure, posing potential risks for people taking blood pressure medications.

L-theanine is generally considered safe, but it may increase drowsiness when combined with certain sleep medications and may also interact with blood pressure medications.

Neither supplement is safe for pregnant or breastfeeding women.

The Food and Drug Administration (FDA) does not test the safety or effectiveness of supplements, including GABA and L-theanine, before they are marketed. Third-party sites like ConsumerLab offer independent tests that can help you make a decision about the right supplements.

Researchers have not studied the long-term effects of stacking GABA and L-theanine.

“Short-term or intermittent coadministration appears to be safe,” Lupu said, adding that it’s important to consult a healthcare provider first given the potential risks associated with these supplements.