Do parents know what their children are listening to when they're blocking them out with their iPod earbuds firmly in place? If they are listening to popular music, chances are high that they are hearing references to substance use.

According to new research presented at the American Public Health Association's annual meeting and exposition in Washington, D.C., 33 percent of the most popular songs of 2005 portrayed substance use.

The study, in which researchers analyzed 279 of the year's most popular songs according to Billboard magazine, also found that allusions to substance use varied widely by genre.

Rap music led the way with 77 percent of songs referring to substance use, followed by country at 37 percent and R&B/ hip-hop at 20 percent. Rock and pop were on the lower end of the spectrum at 14 percent and 9 percent, respectively.

Alcohol and marijuana were the substances most frequently portrayed. The majority of songs with substance use portrayed more positive than negative consequences of use.

Substance use was commonly associated with partying, sex, violence and/or humor, and was most often motivated by peer pressure, social pressure, sex and/or money, for instance, through trafficking.

When children and teens listening to more than 12 hours of music a week, on average, these messages of substance abuse are blaring at them at a high rate.

Experts suggest parents should monitor their children's music choices just as they would television or movie selections.

This story is provided by State Point Media.