Value tracked	Effect size d (λ, p, σ change)	Effect size d (λ, p, σ change)
	200 mg Caffeine (n=1, m=50)	500 mg L-theanine (n=1, m=50)
Log-score substance prediction^[1]	-0.6	-0.7
Absorption	0.61 (λ=13.3, p=0.00017, -0.072)	0.04 (λ=1.38, p=0.77, -0.07)
Mindfulness	0.58 (λ=11.8, p=0.0007, 0.021)	0.12 (λ=0.72, p=0.89, -0.018)
Productivity	0.58 (λ=28.9, p=1.3^-12, 0.11)	-0.28 (λ=5.51, p=0.109, 0.03)
Creativity	0.45 (λ=51, p=4.6^-27, 0.09)	-0.12 (λ=5.05, p=0.14, -0.04)
Happiness	0.27 (λ=10.6, p=0.002, 0.3)	0.16 (λ=3.98, p=0.27, -0.155)
Contentment	0.13 (λ=7.66, p=0.02, 0.47)	0.25 (λ=6.83, p=0.04, -0.04)
Relaxation	-0.11 (λ=5, p=0.15, 0.42)	0.12 (λ=1.5, p=0.74, 0.02)
Chastity^[2]	-0.14 (λ=1.9, p=0.64, 0.11)	-0.03 (λ=1.15, p=0.8, 0.25)
Flashcard ease	0.003 (λ≈∞, p≈0, -0.009)	-0.072 (λ=∞, p≈0, -0.01)
Flashcard ease factor	-0.039 (λ≈∞, p≈0, -32.7)	0.0026 (λ=∞, p≈0, -18.9)
Flashcard new interval	0.011 (λ≈∞, p≈0, -1.88)	-0.016 (λ=∞, p≈0, 3.1)
Time per flashcard^[3]	0.006 (λ≈∞, p≈0, 273.4)	0.003 (λ=∞, p≈0, 13.66)

L-Theanine is synergistic with caffeine in regards to attention switching^[318] and alertness^[319]^[320] and reduces susceptibility to distractions (focus).^[320][321] However, alertness seems to be relatively subjective and may not be a reliable increase between these two compounds,^[318] and increases in mood are either present or absent.^[322]^[318]^[323] This may be due to theanine being a relatively subpar nootropic in and of itself pertaining to the above parameters, but augmenting caffeine's effects; some studies do note that theanine does not affect the above parameters in and of itself.^[324] Due to this, any insensitivity or habituation to caffeine would reduce the effects of the combination as L-theanine may work through caffeine.
L-Theanine does not appear to be synergistic with caffeine in regards to attention to a prolonged and monotonous task.^[325]

—Kamal Patel, “Caffeine”, 2023

See also Examine, Wikipedia and Gwern.

Sitiprapaporn et al. 2018 test the effect of an unspecified quantity of L-theanine via Oolong tea on meditation on 10 university students (non-randomized, it seems). Data collected via EEG and indicates statistically significantly more alpha waves during meditation (although it is unclear how long the meditation was).

This paper is bad. The english is so horrendous it feels like I'm having a stroke while I'm rea...

Jacob Sharf

Jacob Sharf