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 glycine and L-tryptophan together?
Tested together, early signs.
As of August 2026, glycine and L-tryptophan have been tested together in 1 trial, in healthy Japanese men with low urate excretion, and the one trial so far came out ahead of placebo. Scored under the same rules as everything here.
4 studies · 1 tested the actual pair · 1 caution
What you’re seeing
- Glycine renders half-there: for sleep, the science is still forming.
- L-tryptophan renders a ghost: for sleep, almost nobody has looked.
- The woven cord is the rare part: one trial gave both together, and the one trial so far came out ahead of placebo.
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
- 2019Crossover trial · healthy Japanese men with low urate excretion · the pair helpedsource
The other 3 studies on file tested each one alone. See all 4 studies
Fair questions
Is it safe to take glycine and L-tryptophan 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
Pairs that have been tested+
- Glycine has been tested with NAC.
These are the combinations someone has actually run a study on. Every other pairing here is air.
Worth knowing+
- Glycine is widely sold as a sleep aid. The human trials behind that come from one research group at Ajinomoto, an amino acid manufacturer, and are described in the company’s own review rather than pooled by independent analysts. We found no independent meta-analysis of glycine for sleep, so there is nothing here we can score.