Flexible Economy is a new enhanced Economy service operating on a single cabin aircraft for customers on our shorthaul network flying to and from London Heathrow.
Although caffeine is generally safe and well tolerated, it can cause side effects when ingested in large doses. Additionally, regular caffeine use can cause dependency, resulting in withdrawal symptoms when caffeine is not consumed. Headaches can be a symptom of either too much caffeine or too little.
You can see that caffeine also causes the brain's blood vessels to constrict, because it blocks adenosine's ability to open them up. This effect is why some headache medicines, like Anacin, contain caffeine -- if you have a vascular headache, the caffeine will close down the blood vessels and relieve it.