title_body: Is it possible to overdose on coffee?
upvoted_answer: Caffeine overdoses and even fatalities linked to caffeine overdoses have been reported and a quick google scholar search will show that it is still an active field of research and new cases are being found.
  A good overview of caffeine overdose can be found on healthline. Some outakes:
  
  Caffeine overdose may occur if you ingest more than [...] 400mg.
  12 oz. black coffee has 260mg of caffeine
  
  Early symptoms:
  
  dizziness
  diarrhea
  increased thirst
  insomnia
  headache
  fever
  irritability
  
  Severe symptoms:
  
  trouble breathing
  vomiting
  hallucinations
  confusion
  chest pain
  irregular or fast heartbeat
  uncontrollable muscle movements
  convulsions
  
  Prevention is kinda obvious, but I will quote it for completeness:
  
  To prevent a caffeine overdose, avoid consuming excessive amounts of
  caffeine. In most cases, you shouldn’t have more than 400 mg of
  caffeine per day and even less if you’re particularly sensitive to
  caffeine.
  
  The short answer to your last two questions is that one can be addicted to or dependent on caffeine. In a 2012 study investigating caffeine dependence they found that a staggering 96% of subjects had withdrawal symptoms when taken off caffeine and thus had a physical dependence. The article goes into a lot more detail for each of your questions and has a few more good references. So if you want to investigate further that I would suggest that as a good jumping of point.