There's a big difference between being a serious coffee drinker and grabbing a latte or iced coffee every once in a while. Aside from a difference in taste preferences (heavy coffee drinkers tend to scoff at anything light and sweet), their caffeine tolerance may vary, too.
You’ve heard it before, but caffeine is a drug, and it’s one that increases attention and fine motor skills. Caffeine stimulates parts of the brain that control attention and concentration, and it acts as a receptor for one of the brain's signaling molecules, called adenosine, James J. Galligan, Ph.D., a professor of pharmacology and toxicology and director of the neuroscience program at Michigan State University, tells SELF. “Just like many other receptors that respond to drugs, the adenosine receptors become less sensitive to caffeine with repeated exposure,” Dr. Galligan says. So the more caffeine that a person has, the less sensitive the adenosine receptors become, building up a person’s tolerance for caffeine.
Read more here: https://www.self.com/story/caffeine-tolerance