Does the human body produce a substance similar to caffeine?

The idea that the human body probably produces a substance similar to caffeine came to my mind after reviewing the literature on the "restless legs syndrome". This syndrome is a disorder in which the afflicted individual feels an irresistible urge to move the legs, generally when sitting or lying down, and especially in bed, at night, just prior to getting to sleep. The patient has an extremely unpleasant deep discomfort inside the calves, requiring that the legs be moved(1). The "restless legs syndrome" has been described in persons who consume a lot of caffeine(2,3), in patients with iron deficiency anemia(4), and in patients with chronic renal failure(5). Since this syndrome occurs in persons who indulge in caffeine consumption as well as in patients with iron deficiency and patients with chronic renal failure, it is tempting to postulate that the human body- in cases of iron deficiency and chronic renal failure -produces a substance similar to caffeine. The following discussion entertains the hypothetical route that might be involved in the formation of this substance.