If caffeine is 1000 mg (that's about 10 cups of coffee) or even more, the same harm as from amphetamine, heart problems, high blood pressure, psychosis, anxiety, etc. You just need to use everything wisely, because you can even poison yourself with water.
After looking at the question, I looked at the person who asked it. Political science is yours. It's like asking what is heavier than a pound of fluff or a pound of metal. In your question, the keyword is effect. So let's figure it out. I googled a little and found out. Dosages when prescribing caffeine should be selected individually. Higher doses for adults inside: single 0.3 g, daily 1.0 g, intravenous: single 0.4 g, daily 1 g. Caffeine has exciting properties, in general, and is physically addictive. Amphetamine also excites, increases alertness, activity, but mental dependence. (Two different things, please note). Amphetamine is prescribed 10mg x 2 per day, hence 20mg amphetamine versus 1g caffeine. Amphetamine causes dry mouth and you can burn out, doing monotonous "stereotyped" things on waste, so it's better to sleep soundly and eat normally. Well, or hammer cocaine (joke. Approx. For the FSKN). This is all information from the internet, of course.