RT Journal Article SR Electronic T1 Tramadol and Abuse Liability in Humans JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 1 OP 1 VO 338 IS 1 YR 2011 UL http://jpet.aspetjournals.org/content/338/1/1.4.abstract AB