US teens are having less sex, doing fewer drugs and smoking fewer cigarettes than those who grew up in the 1990s, a study released today by the Centres for Disease Control and Prevention has found.

They are also more likely to use condoms when they do have sex, wear a seat belt and avoid getting into a car with a driver who's been drinking, the national study of youth risk behaviour found.

About 48 per cent of high school students were no longer virgins in 2007, down from 54 per cent in 1991.

Meanwhile, just 15 per cent said they'd had four or more sexual partners, down from 19 per cent in 1991.

And 62 per cent of sexually active students said they'd used a condom the last time they had sex, up from 46 per cent in 1991.

Some 35 per cent of teen had at least one drink of alcohol in the month before they were surveyed in 2007, down from 42 per cent in 1991. Recent marijuana use had fallen to 20 per cent of students from a peak of 27 per cent in 1999 while hamphetamine use is down to four per cent of teens surveyed in 2007 from 10 per cent in 2001.

Nearly half as many students admitted to carrying some kind of weapon: 17 per cent in 2007 compared with 33 per cent in 1991. But there has been little change in the number of students who said they'd stayed home from school because they felt unsafe either in the building or on the streets: seven per cent in both 1991 and 2007.

Only 12 per cent of students said they'd rarely or never worn a seatbelt in 2007, down from 35 per cent in 1991.