▁ 2 4   hour ▁ur inary ▁ ▁concentration ▁among ▁participants ▁following ▁just ▁ 3 0   min utes ▁of ▁inten se ▁exercise ▁increased ▁by ▁ 7 7 % ▁relative ▁to ▁bas eline ▁concentr ations ▁in ▁rest ing ▁control ▁subjects ; ▁the ▁reviews ▁suggest ▁that ▁phen eth yl am ine ▁synth esis ▁sharp ly ▁increases ▁while ▁an ▁individual ▁is ▁exer cis ing , ▁during ▁which ▁time ▁it ▁is ▁rapidly ▁met abol ized ▁due ▁to ▁its ▁short ▁half - life ▁of ▁roughly ▁ 3 0   seconds . ▁In ▁a ▁rest ing ▁state , ▁phen eth yl am ine ▁is ▁synth es ized ▁in ▁c ate ch ol am ine ▁neur ons ▁from ▁ ▁by ▁a rom atic ▁am ino ▁acid ▁dec ar box yl ase ▁( A AD C ) ▁at ▁approximately ▁the ▁same ▁rate ▁at ▁which ▁dop am ine ▁is ▁produced . ▁ ▁In ▁light ▁of ▁this ▁observation , ▁the ▁original ▁paper ▁and ▁both ▁reviews ▁suggest ▁that ▁phen eth yl am ine ▁plays ▁a ▁prominent ▁role ▁in ▁medi ating ▁the ▁m ood - en han cing ▁eu ph or ic ▁effects ▁of ▁a ▁runner ' s ▁high , ▁as ▁both ▁phen eth yl am ine ▁and ▁am ph et am ine ▁are ▁pot ent ▁eu ph ori ants . ▁▁ β - End orph in ▁▁ β - End orph in ▁( cont ract ed ▁from ▁" end ogen ous ▁morph ine ") ▁is ▁an ▁end ogen ous ▁op io id ▁ne urope pt ide ▁that ▁bind s ▁to ▁ μ -