Caffeine can be a headache trigger or headache inhibitor. Caffeine can be found in beverages, chocolate and even in some popular over-the-counter and prescription pain relievers. Before a headache or migraine, blood vessels tend to enlarge. Because it contains “vasoconstrictive” properties that cause the blood vessels to narrow and restrict blood flow, caffeine can aid in head pain relief. When caffeine is added to the combination of acetaminophen and aspirin, the pain relieving effect is increased by 40%.