Why would one medicine work differently than another medicine?

C. Thomas Wild learns that caffeine works for his Inattentive ADHD from birth. - NoDoz.

Why does a second caffeine product work differently - Tirend?

The surprising, true story:

https://cthomaswildadhdreductionadhdauthor.video.blog/2019/11/14/welcome-to-the-c-thomas-wild-adhd-reduction-adhd-author-blog/

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Caffeine works for ADHD;  food additives in FDA approved medicines and foods need better ingredient labels.

- C. Thomas Wild (1981, 2020)