What do the states mean?+
- Solid: well studied, and it works.
- Half-there: the science is still forming.
- A ghost: almost no real studies.
- Hollow: well studied, and it does not work.
- A cord: the pair itself has been tested together.
- Air: nobody has ever tested this pair.
The full scoring method: How we score
Can you take L-theanine and L-arginine together?
You don’t need to take them together.
As of August 2026, L-theanine and L-arginine have been tested together in 1 trial, in healthy young adults, and no clear added effect was found. Scored under the same rules as everything here.
38 studies · 1 tested the actual pair · 1 caution
What you’re seeing
- L-theanine renders solid: for sleep, it is well studied and it works.
- L-arginine renders half-there: for endurance, the science is still forming.
- The woven cord is the rare part: one trial gave both together, and no clear added effect was found.
You can tell before you read a word.
Magnesium + L-theanine are sold together in the same aisle. No trial has ever tested the pair. When that is true, we draw nothing between them. The nothing is the review.
The pair trial
- 2022Randomized trial · 120 people · healthy young adults · no clear effectsource
The other 37 studies on file tested each one alone. See all 38 studies
Fair questions
Is it safe to take L-theanine and L-arginine together?+
The studies on this page gave both together and reported no harm from the combination. That is not the same as a safety trial, and it says nothing about your dose or your medication.
How many studies is this based on?+
1 that gave the pair together. The papers are listed above with links to the source.
Deeper
What each one is on its own+
L-theanine
- Sleepsolid
- Memory and focushalf-there
- Moodhalf-there
- Stress and anxietyhalf-there
L-arginine
- Endurancehalf-there
- Asthma and breathinghalf-there
- Blood pressurehalf-there
- Cholesterolhalf-there
- Gut and digestionhalf-there
- Hearthollow
- Immunity and coldshalf-there
- Inflammationhalf-there
- Performance and vitalityhalf-there
- Pregnancya ghost
- Sprint and repeated-effort powerhalf-there
- Strength and powerhalf-there
- Testosterone and libidohalf-there
- Weight and body fathollow
- Wound healinghalf-there
Pairs that have been tested+
- L-theanine has been tested with green tea extract, chamomile.
- L-arginine has been tested with creatine monohydrate, selenium, L-lysine, L-glutamine, probiotics, vitamin C.
These are the combinations someone has actually run a study on. Every other pairing here is air.
Worth knowing+
- L-arginine: Searching 21 health outcomes returned no trial of L-arginine on its own for any of them. This is not the same as a supplement nobody has studied. L-arginine is a nutrient your body needs, and there is research on it. What that research is about is multi-antioxidant fertility formulations and clinical nutrition, rather than arginine taken alone. None of it tells you whether taking extra helps someone who already gets enough.