How Running Makes you High

          When you run at 80% of your maximum heart rate for about 30 minutes your body forms to mood modifiers, Endorphin and Anandamide. Endorphin is actually an Opioid which is a name for a number of chemical substances that act like Morphine in the human body. Opioids are also used in anesthetics and pain relievers. Going back to the Endorphin and Anandamide. Anandamide is similar to THC which is the main element of Marijuana. Your blood flow carries the two chemicals to your blood brain barrier. at this point they are basically at the gate to brains blood system. Anandamide passes easily because its small but the Endorphin is bigger and therefore its harder for it to pass. But don't worry your brain produces Endorphin.

          The two chemicals are now tapped into your main nervous system were they limit the signaling power of pain sensors called Nociceptors that spread out through your spinal-cord. As a result of this you don't really realize how much your legs are burning. The Endorphin downshifts you pre-frontal and limbic regions which control  your emotion and motivation. You now become calm and comfortable, and as more Endorphin kicks-in you might even in some cases feel euphoric.
          Anandamide triggers the release of Dopamine, a neurotransmitter that controls the lust, pleasure, and addiction. It also binds to cannabinoid receptors in your brains pleasure circuit where it sends bliss vibes for minutes and even hours. Bliss vibes in figure 1

figure 1