Historically part of Midlothian, the city has long been a centre of education, particularly in the fields of medicine, Scots law, literature, the sciences and engineering. The University of Edinburgh, founded in 1582 and now one of four in the city, was placed 17th in the QS World University Rankings in 2013 and 2014. The city is also famous for the Edinburgh International Festival and the Fringe, the latter being the world's largest annual international arts festival.
Onset and Duration. It takes approximately 15 to 45 minutes for caffeine to reach its peak levels in your bloodstream. Caffeine has a half-life of approximately five to six hours, meaning that it takes this long for its concentration in your bloodstream to reduce by half.
It is the world's most widely consumed psychoactive drug. Unlike many other psychoactive substances, it is legal and unregulated in nearly all parts of the world. There are several known mechanisms of action to explain the effects of caffeine. The most prominent is that it reversibly blocks the action of adenosine on its receptor and consequently prevents the onset of drowsiness induced by adenosine. Caffeine also stimulates certain portions of the autonomic nervous system.