Evidence-graded answer
Can I drink coffee on GLP-1?
Yes. There is no interaction between caffeine and GLP-1 medications. Some patients find coffee on an empty stomach is harder to tolerate during titration weeks (more nausea); switching to coffee with food, or temporary reduction, usually solves this.
Caffeine does not alter GLP-1 absorption or efficacy.
Caffeine on an empty stomach + delayed gastric emptying can amplify acid reflux. Many patients find half-caf or coffee with breakfast more comfortable.
Hydration matters more on GLP-1 than caffeine intake. Aim for at least 2 L water/day during titration weeks.