Black Coffee Side Effects: Black coffee, when consumed in excess, can lead to various side effects. It is known to cause insomnia, as its high caffeine content can disrupt sleep patterns. Additionally, excessive intake of black coffee can result in increased heart rate, palpitations, and heightened anxiety levels. It may also lead to gastrointestinal issues such as acid reflux, stomach ulcers, and irritable bowel syndrome. Regular consumption of black coffee can stain teeth and cause bad breath. Moreover, it can contribute to dehydration due to its diuretic properties. Individuals with certain health conditions like high blood pressure, heart problems, and anxiety disorders should be cautious when consuming black coffee.