Emory University researchers found 32 percent of African-American girls using marijuana had incident STDs compared to 23 percent of non-marijuana users. The marijuana users were also more likely to have more partners and riskier partners such as some recently released from jail or under the influence.

"While adolescent African-American females remain a high-risk group for STDs, little research has examined their marijuana use, sexual behaviors and incidence of STD infection," study co-author Ralph DiClemente of Emory's Rollins School of Public Health in Atlanta said in a statement. "Although no differences in condom use were identified between marijuana users and non-users, results suggest that marijuana users are engaging in sexual acts with riskier partners and under riskier circumstances, and had higher rates of STDs."

The study compared marijuana use and self-reported sexual behavior in 339 sexually active African-American females between the ages of 15 and 21.

The researchers are presenting their findings at the International AIDS Conference being held in Mexico City.