sleep
Excess caffeine can overstimulate the central nervous system. High amounts of caffeine produce negative effect on sleep on set and quality[20]. However, there are large individual differences in the effects of caffeine on sleep. Many people consume coffee during the evening and have no problems falling asleep. Some people find that the mild stimulation of caffeine consumed shortly before a bed time delays the time to fall asleep.
8 Heartburn
Some people suffer from heartburn after drinking coffee. Coffee promotes gastro-oesophageal reflux, but is not associated with dyspepsia.
9 Dehydration
The caffeine in coffee is a mild diuretic and can increase the volume of urine excreted. However, this effect can be easily counteracted by the drinking extra glass of water.