Sex abstinence programmes do not stop risky sexual behaviour or help in the prevention of unwanted pregnancy, a research team has concluded.
Sex abstinence programmes are popular in the US
The Oxford University team reviewed 13 US trials involving over 15,000 people aged 10 to 21.
They found abstinence programmes had no negative or positive impact on the rates of sex infections or unprotected sex, the British Medical Journal said.
Abstinence programmes are popular in the US and have supporters in the UK.
A UK branch of the US Silver Ring Thing was set up four years ago to promote sexual abstinence among young people.
However, such groups have so far failed to gain the foothold they have in the US where a third of the President's HIV budget is given to abstinence programmes.
The latest study, which included trials comparing young people attending abstinence-only programmes against those receiving no sex education, raises questions over whether they work in developed countries.
Researchers found none of the abstinence-only programmes had an impact on the age at which individuals lost their virginity, whether they had unprotected sex, the number of sexual partners, the rates of sexually transmitted diseases or the number of pregnancies.
One trial did show a short-term benefit with participants reporting that they were less likely to have had sex in the month following one abstinence-only programme.
But the researchers said this finding was offset by six other trials that showed the programmes had no effect on the participants' recent sex lives.
Another trial even showed that participants in abstinence-only programmes were significantly more likely to report pregnancy and sexually transmitted disease, compared to participants using the usual services.
However, other studies did not show this.
This compared to programmes that promote the use of condoms which greatly reduce the risk of HIV, the BMJ reported.
Lead author Kristen Underhill said: "Our analysis suggests that abstinence-only programmes that aim to prevent HIV are not effective.
"This finding has key implications for policy and practice, especially in the US, where abstinence-only programmes receive both federal and state funding."
Genevieve Clark, of the Terrence Higgins Trust, said: "Young people need to know that they can say no to sex, just as they need to know how to protect themselves from pregnancy or sexually transmitted infections if they decide that a sexual relationship is right for them.
"But abstinence-only programmes don't work because they provide no safety net for those young people who do have a sexual relationship - and research shows that many do."
And Ivan Blake, of the young people's sexual health charity Brook, added: "There are even studies which show they can make things worse as people do not have the knowledge or confidence to have safe sex."