The article does imply that he was drunk off alcohol, in addition to the sleeping pill.
A few hours later, (about 6 after drinking all of the Mountain Dew,) I pooped. As everything moved in my insides, the caffeine finally hit me all at once.
So it's completely possible for a sleeping pill to sit in Well's stomach for a few hours before he finally absorbed it. I wouldn't attribute any malintent on his part here.