Question: Can I Drink Coffee Before Running?
"I like to drink coffee in the morning. Can I have a cup of coffee before my long runs?"
Answer: Some people drink coffee before runs and never have any issues with it, but others experience GI issues. If you can tolerate it and actually need coffee to get you going in the morning, then keep enjoying it before your runs. Pre-run caffeine has been shown to enhance performance and endurance, so you may notice a little boost during your runs. However, if you're doing a race of 10K or longer, don't consume more than 200 mg of caffeine (about 2 cups of coffee). Some experts believe too much caffeine may increase risk of cardiac events while running.
Also keep in mind that coffee is a mild diuretic (makes you have to urinate), so it's not the same as hydrating with plain water. If you want a pre-run cup of coffee, drink it early enough that you'll have time to use the bathroom, so you can avoid stopping to urinate during your run.
More: Nutrition and Hydration for Long Distance Running
Maharam, Lewis, M.D., et. al. "IMMDA's Health Recommendations for Runners and Walkers" March 20, 2010