N-of-1 Blinded Experiment: Will 210mg L-Theanine Reduce my Coffee-Induced Anxiety?
resolved Dec 7

Randomised trials have suggested that L-Theanine meaningfully reduces the anxiety-inducing effects of caffeine, while maintaining its cognitive benefits.

I will be undertaking a blinded trial with L-Theanine using the following protocol:

1. Take 210mg L-Theanine or a placebo (blinded) just before my morning small iced coffee.

2. 90 mins after coffee consumption, I will record my anxiety level as a subjective measurement between 0-10.

3. Repeat for 20 days during which I will engage in sustained periods of focused work.

(Protocol taken from here, which has sources: https://n1.tools/experiments/anxiety/lTheanine)

Resolution criteria: Resolves YES if a naive model (i.e. that doesn't include confounders etc.) suggests at least an 80% probability that consuming L-Theanine reduces anxiety.

In other words: "Compared to placebo, a difference in anxiety between -xx% and 0% is at least 80% likely".

For reference, my previous market on whether L-Tyrosine improves focus used 20 data points and resulted in mean focus (placebo) of 7.4 and mean focus (L-Tyrosine) of 7.0. The model suggested that "Compared to placebo, a difference in focus between 0% and 30% is 19.4% likely". Image from that experiment below.

Extra notes:
- Starting this experiment today.

- I may visit different cafes, but I'll always order a small iced coffee and try my best to consume about the same amount of caffeine each day (without being too strict).
- I won't bet on this market.
- I am sensitive to caffeine and do experience quite pronounced caffeine highs and lows.
- Dosage is 210mg because the brand I use from Amazon provides 210mg capsules (they suggest two capsules per dose).

Model details (for those interested)

I'll model the posterior distribution of anxiety values with the placebo and with L-Theanine, and then merge those to create a posterior distribution for the % difference in anxiety between the two. I'll be using a Bayesian model for this, which requires a prior to update. That prior will be the mean anxiety for the placebo and L-Theanine from the data itself (which is informative, and means the data will basically define the posterior distribution).


Mean L-Theanine ~ Normal(mean_data, std_data)

Mean Placebo ~ Normal(mean_data, std_data)

StdDev L-Theanine ~ HalfNormal(5)

StdDev Placebo ~ HalfNormal(5)


Data L-Theanine ~ Normal(Mean L-Theanine, StdDev L-Theanine)

Data Placebo ~ Normal(Mean Placebo, StdDev Placebo)

Deterministic Transformation for Percentage Difference:

Percent Difference = ((Mean L-Theanine - Mean Placebo) / Mean Placebo) * 100

Posterior Inference:

Probability(Percent Difference ≤ 0) ≥ 0.80

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Seems like L-Theanine works to reduce post-coffee jitters!

Mean post-coffee anxiety with L-Theanine: 4.2
Mean post-coffee anxiety without L-Theanine: 5.0

82.6% chance of an anxiety reducing effect (honestly higher than I expected).

(Note: I updated my app to use Absolute Difference on the KDE plot x-axis but for the resolution of this market quickly switched the analysis back to Percent Difference, so ignore the x-axis label)

I bet NO because I thought 83% chance of effect was pretty high. I think there’s more than a 17% chance of no effect, let alone potentially negative effects or different kinds of anxiety. I’ve heard anecdata about L-theanine giving a different sort of anxiety that is still edgy despite being less jittery than caffeine, so increased total anxiety also seems possible to me.

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