Start with timing. If you want daytime clarity, keep coffee earlier and pick a smaller, smoother cup (paper-filtered drip or pour-over tends to be kindest). If your goal is sleep, take the antihistamine in the evening and keep afternoon coffee light—or choose decaf/half-caff. Next, consider the stomach. Both caffeine and anticholinergic antihistamines can dry you out a bit; sip water as your default sidecar and avoid big, fast gulps of very hot coffee. Finally, pick beans that are friendly to your goals: low-acid decaf or balanced half-caff for calmer stomachs and steadier nerves; smooth medium roasts if you tolerate caffeine well.