Although some chemicals in coffee are carcinogens in rodents at very high doses, research suggests that they are not dangerous at the levels consumed by humans.[134] Instant coffee has a much greater amount of acrylamide than brewed coffee.[135] Research suggests that drinking caffeinated coffee can cause a temporary stiffening of arterial walls.[136] Coffee may aggravate pre-existing conditions such as gastroesophageal reflux disease, migraines, arrhythmias, and cause sleep disturbances.[137]

Caffeine can cause anxiety, especially in high doses and in those with pre-existing anxiety disorders.[138][139]