Consequences. their are many but only for specific cases.
in general the minor ones are that if your mana reaches zero you will be much more vulnerable to magical attacks in a way that could disable your ability to interact with magical phenomena in fact your overall magic capability can be lowered if attacked while having no mana. this is easily avoidable and one can even recover from damage to their magical essence if they put in the work to recover. recovering in this instance however is similar to exercise but like if your were 70 pounds overweight. The usage of magic dynamically lowers your Aura which is your ability to influence your surroundings passively and also hide your magical signature. the last minor yet subtle consequence to using magic is that it has a slightly sexually arousing quality to casting which invite different sets of implications depending on the type of magic being used, this effect can be ignored for more precision in casting but letting it "take you" yields more power output.
median consequences are heat and flux
heat is actually the least worrisome. if a spell or magic phenomena causes too much heat and the user is not up to par to handle it they can definitely burn themselves with mana flames. mana flames may burn your arm off or any other body part but sleeping will fix it completely. it is not the same as a physical burn though it will be perceived as one. non-living objects burned by mana flames will disappear completely,sometimes even from memory.
flux is basically a sudden infuse of magical energy usually from the environment. it can make a spell unexpectedly 3 to 10 times as powerful as it would normally be. flux generally happens in areas near magically saturated zones but its not unheard of for low flux phenomena to happen in "magically null" areas. experienced casters have a sense for flux so it is not as dangerous when they experience flux. heat and flux often occur together but can be exclusive phenomena.
Major consequences of magic use come from specific situations.
usage of magic within a magically saturated zone for too long
usage of "corrupting magic" which are spells designed to take from the user
usage of "junk magic" which are spells that are hollow in effectiveness or highly temporary
In a magically saturated zone the free flowing mana can alter the type of magic a person casts, this can be permanent if they stay long enough.indecently these are also areas of high flux as well. "Mana chasers" are those of low magical ability or no magical ability who frequent these zones these zones order to obtain higher magical ability but often cases some magical ability because they may have none magically saturated zones are often marked by townspeople or city regulators. unmarked zones are noted by the high color saturation seen dripping and evaporating on grass, rocks and other objects in that area. essentially anything that glows as if it has just been painted can be assumed to be magically saturated. animals play a special role in relieving and distributing magical saturation across ecosystems.
as far as immediate consequence for magic use, there is none somewhat. as long as you are within the safe zones you will experience mild yet fleeting sexual arousal and creativity. yes it is something you can get addicted to in the sense that you can get addicted to eating or gaming. but thats about it.