WASHINGTON (Reuters) - They have lyrics such as "Tequila makes her clothes fall off" and "Breakin down the good weed, rollin' the blunt/Ghetto pimp tight girls say I'm the man."

U.S. popular music is awash with lyrics about drugs, alcohol and tobacco. Medical researchers have reviewed the words of the 279 top songs of 2005 to estimate just how common they are.

Their report Monday showed a third of the songs had explicit references to substance abuse. And two-thirds of these references placed drugs, alcohol and tobacco in a positive light by associating them with sex, partying and humor, according to the team led by Dr. Brian Primack of the University of Pittsburgh School of Medicine.