By 2pm, your coffee doesn't seem to do much anymore. You're not imagining it.
Caffeine works by blocking adenosine, a chemical that builds up in your body through the day and makes you feel tired. Early in the day, adenosine levels are low, so caffeine has a clear target to block. By the afternoon, adenosine has been building for hours — there's simply more of it, so the same amount of caffeine has less to work with.
This is separate from tolerance, which builds over weeks of regular caffeine use. The afternoon dip happens every single day, tolerance or not — it's about timing, not habit.
A few things help: spacing your caffeine out rather than front-loading it, or having a smaller, more precise amount later in the day rather than another full coffee. That's part of why we built Neuchu as a 50mg-per-piece gum — it's easier to have a controlled top-up in the afternoon without committing to a whole second coffee. You can find it here.