From a 2018 review and case study on the clinical toxicology of caffeine in the Journal of Toxicology Reports, on negative side effects of caffeine:
“Some features can include hypokalemia, anorexia, nausea, vomiting, palpitations, seizures, dysrhythmia and a constellation of symptoms, referred to as “caffeinism”, which is apparently indistinguishable from severe chronic anxiety.”
And the CDC and the FDA have a lot to say about caffeine and energy drinks, too:
Caffeine overdoses and emergency responder training (CDC)
Energy drinks in schools (CDC)
Archive for high-concentration caffeine supplements (FDA)