I agree it is the caffeine. I was at my inlaws once and developed a whopper of a headache that wouldn't go away. I was maxing out my Tylenol limits with no relief. My MIL asked me if I drank a lot of coffee at home. Yep. She informed me that theirs was decaff because of FIL's cholesterol levels! We made an emergency visit to Starbucks! I was cured. Wean yourself slowly to avoid the headache. Mine was crippling.