That said:
- I'm middle aged and have had tens of thousands of cups of coffee
- The difference is pronounced, not subtle
- It's well-studied https://pubmed.ncbi.nlm.nih.gov/18296328/
FWIW, I've played around with a lot of supplements. Generally the effects are non-existent or subtle. I'm not generally given to a placebo effect wrt this kind of stuff
Biggest issue I think would be making sure that there aren't any tells like flavor or some quality of the additive.
Brew identical looking bottles of cold brew. Label the bottoms 1 through whatever. Mix them up. Label the lids A through whatever. Probably need to add some creamer to mask any possible sediment. Drink from them throughout the week. Note the lid label and your reaction. At the end of the test period look at the bottoms of the bottles to correlate the controls and placebos with your experiences.
I personally don't feel the need with this particular thing though. It's a fairly pronounced difference.
It's also not really susceptible to the placebo effect IMO. Could I imagine some vague promised positive effect? Absolutely yes. Could I imagine the erasure of jitters? I don't think I could placebo that away.
Anyway as linked in another post this is well-studied.