Gwern has an extensive write up on melatonin at https://www.gwern.net/Melatonin https://www.gwern.net/Melatonin Personally if I'm off caffeine for too long the

Gwern has an extensive write up on melatonin at https://www.gwern.net/Melatonin https://www.gwern.net/Melatonin Personally if I'm off caffeine for too long the resulting metabolism strangeness takes me out for about a day, but the next time that happens I'm going to try a good amount of water and salt to see if that can combat it. Probably something around 1L/6g salt. Other things to consider with caffeine: adding l-theanine to temper the jitters. [ Search for l-theanine caffeine stack for other information on this. ] Exercise definitely helps with concentration. I believe that it was only recently "discovered" that the brain is a giant lymph node and the only times it appears to be able to clear the decks of waste are when you're asleep or when you're pumping blood with a good exertion. [ http://www.nature.com/nature/journal/v523/n7560/full/nature14432.html http://www.nature.com/nature/journal/v523/n7560/full/nature1... ]