Following what is thought to be the biggest review of existing studies into internet use and young people, the researchers suggest that, in future, clinical assessments of such young people should include questions about the online content they have viewed.

The global review, published in the journal PLOS ONE, shows that young people at risk of self-harm or suicide were often online for longer periods than other teenagers. The Oxford team analysed a total of 14 studies and found contradictory findings on whether the internet exerted a positive or negative influence. Some studies found that internet forums supported and connect socially isolated people, helping them to cope. But other studies concluded that young people who went online to find out more about self-harm and suicide were exposed to violent imagery and acted out what they had seen online. The review finds that internet use is linked with more violent methods of self-harm.

Moderate or severe addiction to the internet is also connected to an increased risk of self-harm, as well as increased levels of depression or thoughts about suicide, according to the Oxford review. The review also says there is a strong link between young people using internet forums and an increased risk of suicide -- a connection not found in relation to other social network sites. In one of the studies reviewed, well over half (59%) of young people interviewed said they had researched suicide online. Meanwhile, of 15 teenagers who had carried out particularly violent acts of self-harm, 80% said they had gone online to research self-harm beforehand. Of 34 who self-harmed by cutting, 73% said they had researched it online.

Young people who used the forums stressed the value of anonymity. One of the studies reviewed suggested that young people using the forums appeared to normalise self-harm. Most users went to the forums for empathy or to discuss safety issues rather than talk about how they could reduce their self-harming behaviour. Another study showed that out of nearly 300 posts, 9% were about methods of self-harm and users went to the forums to swap tips on how to hide the problem.

Internet forums did not make the users feel any better, and in some cases they showed signs of increasing distress after using the sites, said one study. However, another study contradicts this, saying that an analysis of the posts created by forum users reveals that by the third month they were less distressed than they had been in the first couple of months. Young people who went to the forums said positive behaviour was encouraged -- they congratulated each other for not cutting or urged one another to seek help from GPs. Despite this, the review says that overall although forums may have provided emotional support, there is no evidence to suggest that this translated into young people actually reducing levels of self-harm. There was no consensus among users as to whether forums altered this behaviour.

The review also highlights the risk of cyber-bullying to vulnerable young people. Online bullying was found to make victims more likely to self-harm. One study suggested that it slightly increased rates of attempted suicide by the victim as well as the perpetrator. Email was used in 18% of cases of cyber-bullying, followed by instant messaging (16%), MySpace (14%) and chat rooms (10%), says the review.

Senior co-author Professor Paul Montgomery, from the Centre for Evidence-Based Intervention at the University of Oxford, said: 'We are not saying that all young people who go on the internet increase their risk of suicide or self-harm. We are talking about vulnerable young people who are going online specifically to find out more about harming themselves or because they are considering suicide already. The question is whether the online content triggers a response so that they self-harm or take their own lives and we have found that there is a link.'

Senior co-author Professor Keith Hawton, from the Centre for Suicide Research at the University of Oxford, said: 'Communication via the internet and other electronic means has potential roles in both contributing to and preventing suicidal behaviour in young people. We are only now beginning to realise the extent of these possible influences and this review is a contribution to this knowledge. The next step is going to be development of therapeutic interventions using these channels of communication, especially to access those who do not seek help from clinical services.'

Lead author Kate Daine, a postgraduate researcher from the Centre for Evidence-Based Intervention, said: 'There are no known online interventions to date that specifically target young people at risk of self-harm or suicide and yet we find that adolescents who self-harm are very frequent users of the internet. While social media might be useful for supporting vulnerable adolescents, we also find that the internet is doing more harm than good in some cases. We need to know more about how we can use social media as a channel to help young people in distress.'

Responding to the review, Joe Ferns, Executive Director of Policy at Samaritans, said: 'We should acknowledge that many people are using suicide forums and chat rooms to anonymously discuss their feelings of distress and despair, including suicidal thoughts, which may have a positive impact on the individual. They may be expressing feelings that they have never disclosed to anyone in their offline lives. Rather than concentrating primarily on ways of blocking and censoring such sites, we should think about online opportunities to reach out to people in emotional distress. However, deliberately encouraging or assisting suicide online is already a criminal offence and, where possible, the authorities should use their existing powers to prosecute malicious individuals who do this.'