If he starts to get really bad cramps in his legs, thats a sign that he's doing it to often. The pain is from Constriction of blood vessles, and its said that in very high doses that morning glories(and HBWR seeds) can cause ergotism (though ive never actually heard of anyone getting ergotism from them.), which can lead to gangreen(not sure i spelled it right), which can lead to loss of extremities... But the cramping is just an early warning sign, nothing to worry about.