It is a drug—it’s a stimulant, which interestingly is in the same category as nicotine (cigarettes/tobacco for those who don’t know), as well as meth and cocaine. Addiction to caffeine is relatively common and unregulated, interestingly enough. Ultimately it’s not the worst thing you could be drinking, but it’s good to remember not to have too much and to try to stay out of making it a daily habit.
Extra fun science fact: I did an experiment with some tiny, see-through arthropods where we measured their heart rate while they were in different substances. Since caffeine is a stimulant, it made their hearts beat faster. Alcohol, on the other hand, is a depressant, and it made their hearts beat slower. (Other depressants include marijuana, morphine, and heroin. Stay safe people!)