Iris (Definition) The iris is a structure within the eye that helps reduce the amount of light that reaches the retina. The iris is known as the colored part of the eye, and can be blue, brown, or any color or combination of colors in between. The iris is the portion of the eye that responds to light stimulation. ...Read more.
Scientists also speculate that caffeine may provide a mood-boosting effect that helps ease pain. Regardless of the mechanism by which it works, the data does indicate that caffeine does indeed make pain medications more effective and help ease pain.
When your body fully uses caffeine, the effects caffeine had will reverse. For example, the blood vessels to your brain and lungs will constrict back to their normal size and those to your stomach will dilate. This can cause you to feel fatigued, have a headache or experience stomach upset. Caffeine affects people differently.