Immune system deficiencies, decreased energy overall, and addiction risks beyond just 'habit forming' to start off. Watching people detox the stuff's no joke, and watching my folks and a roommate of mine try going cold turkey was enough to inspire me to do a project on it for my 'Psychology of Addiction' class years back (I also got to see Systematic try to kick the stuff when we went to Thailand, a place that refuses to sell caffeine).
Caffeine's up there with salt, dairy, and sugar when it comes to addictive food sales, and it hits harder than those do. Typically with how they package it it's delivered to the person in drink-form... but caffeine is also a diuretic, meaning that you're actually becoming more dehydrated through it's consumption. With the energy it works up as well you'll be burning through your stores of water much faster, and as we've seen with energy drinks this can lead to a vicious cycle similar to that of Salt and Alcohol, both for the endless cycle and through how it can trick the reward center of your brain. These cycles can lead to organ failures of various kinds, including the liver.
Caffeine's a mess, it's best you quit that shit beyond occasional use. For myself it's worse than it is for other people over how it can make my schizo-symptoms harder to control, but witnessing it from others doesn't look fun either as they become adjusted to it, as they require it to 'feel normal'. It's not as bad as cigarettes, but it's an over the counter drug sold to us in the form of food and drink (and even soap). Their body gets this like... itch for it as their blood pressure and REM cycles get all fucked up without it.
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