Caffeine is a drug used world round for energy, mental alertness and even weight loss. It’s found in coffee, tea, energy drinks, and more. Caffeine is also addictive and can be extremely dangerous in high amounts, for the average person who may only drink up to 3 cups a coffee per day, caffeine is usually safe.
The list of side effects includes but isn’t limited to
Blood in the stools or urine
Burning feeling or tenderness in the stomach
Coughing or vomiting blood
Swelling of the face, ankles, or hands
Unusual tiredness or weakness
Vomiting of blood or material that looks like coffee grounds
https://www.drugs.com/sfx/caffeine-side-effects.html
https://www.webmd.com/vitamins/ai/ingredientmono-979/caffeine