I made an app for this called Reflect [1]. You can run self guided experiments for anything you can model as a metric in the app. I just wrote about an experiment I did with nootropic coffee [2].

[1] https://apps.apple.com/us/app/reflect-track-anything/id64638...

[2] https://open.substack.com/pub/reflectapp/p/my-experience-wit...