New York, Oct 8 (IANS): Undergraduate college students are more likely to have unprotected sex on days they use marijuana or binge on alcohol than on days they don't, warns a study.

Binge drinking and being in a serious dating relationship were linked to less condom use, putting young adults at risk for sexually-transmitted infections and unplanned pregnancies, the study said.

The findings draw attention to some common but risky sexual behaviours in college students, said study's lead author David Kerr.

"People may judge risks, such as whether they will regret having sex or whether they should use a condom, differently when they are drunk," said Kerr, an associate professor in the school of psychological science at Oregon State University.

Having sex without a condom is considered risky behaviour because condoms are the only way to protect against STIs, including HIV.

For the purposes of the study, binge drinking was defined as four or more drinks for women and five or more drinks for men.

For the study, the researchers recruited 284 college students who reported their marijuana use, alcohol use, sexual activity and condom use every day for 24 consecutive days.

One goal of the study was to examine marijuana use, which rarely has been studied in relation to risky behaviour.

"College students were more likely to have sex on days they used marijuana, but we didn't find a connection between marijuana use and poor condom use," he said.

The study also compared the sexual behaviour of college students who were single versus those who were seriously dating someone.

"Two findings stood out. Students in serious relationships had almost 90 percent of the sex reported in our study. But serious partners used a condom only a third of the time, compared to about half the time among single students," Kerr said.

The findings were published in the Journal of Studies on Alcohol and Drugs.