@ysmina-- That might be the effect of caffeine alone, but when taken with aspirin, the effects are different. Caffeine makes our heart beat faster which means that blood flows throughout the body at a faster rate. Aspirin is not just a pain reliever, but also a blood thinner. So when someone takes aspirin with caffeine, the pain reliever circulates through the body very quickly.
This is why many people take an aspirin followed by a cup of coffee after a hangover. It relieves headaches very quickly.
The downside is that caffeine is diuretic and will expel water from the body through urine. So if you take aspirin and caffeine together, you need to drink plenty of water to avoid being dehydrated.
The more serious risk is damaging the liver. Caffeine gets metabolized in the liver, just like medications. So aspirin plus coffee will put a strain on the liver. And if someone is hungover and the liver is still processing alcohol, that's a lot of work for one liver to do. So aspirin and caffeine is not a combination that you want to take everyday. If you're healthy, you can take it once in a while but don't overdo it.