In which case, it depends on the type of inhibitor. A competitive inhibitor has a structure similar to the substrate, hence would bind to the active site as well, competing with the substrate for the enzyme active sites, decreasing enzymatic activity. A non-competitive inhibitor binds to the allosteric site of the enzyme, causing a structural change in the enzyme active site shape.
There's a difference between the effects of cold-brewed coffee vs. hot-brewed coffee: because different chemical reactions are achieved at higher temperatures, cold-brewed coffee will have a smoother caffeine effect and overall less acidity, which some people experience as part of the kick..
Depends on amount: Caffeine is a stimulant. Small amounts can improve alertness and motor function. High doses can cause tremors and excessive movements. Different people have different reactions. Usual coffee contains 120mg per cup. A large starbucks can have 320mg.