This entirely depends on what the risk behavior is. But most of the negatives are addiction, jail, behavior problems, loss of control, sometimes depression or suicidal incidents, crashes, and sometimes life threatening situations. Drugs, alcohol, steeling, vandalism, gangs, fights, and other activities are the most troublesome to deal with. Hope this helped.
There can be quite a lot of negative impact from youth risk behaviour, I think. It does depend on what the risk behaviour is though.
The image above shows you some of the risk behaviour that youths engage in. I would say another risk behaviour is taking part in criminal activities such as shop lifting and joyriding.
So, what are the negative impacts of youth risk behaviour?
Unwanted sexually transmitted infections, or even a baby...
If youths are having sex when they are too young to be sensible and are taking risks, chances are something bad is going to happen. IF they're not using condoms, this can include getting STIs such as chlamydia or gonorrhoea, which are beginning to become resistant to antibiotics because of how fast they are spreading.
Another impact of having risky sex is ending up with a baby, which is not great when you're young and still have loads of fun to have before you settle down.
Having to go to hospital
Youths often like to drink, and being too young to know their limits, often end up being very, very ill. It's really not cool. At best, they're in the bathroom all night with their head down the toilet. At worst, they're in hospital on IV drips and having their stomachs pumped. This can happen with illegal drugs too - if adults' bodies can't process them well, young people's bodies are even less equipped to handle them.
Ending up with an addiction
You start as you mean to go on. If youths start drinking, smoking and taking drugs at a young age, and keep up the habit into their early adult life, it becomes more and more difficult to stop. They might find that once they've had enough of their risky lifestyle, it's too late and they end up addicted to alcohol, nicotine or other drugs. The further negative impact of this is, of course, is that these addictions can lead to all sorts of health problems as they get older, such as heart disease, liver failure or cancer. Luckily, a lot youths grow out of the habit before it can go too far.
Ending up in prison...
They're not called 'risk behaviours' for no reason. If youths are taking the risks of dealing illegal drugs, shoplifting, joyriding, or even doing anything stupid under the influence of alcohol, there may come a time when they get caught. Whilst the thrill of doing whatever it is probably feels great, I doubt prison is that awesome. By the time a youth is 16 they can start getting hefty sentences, and a criminal record seriously impacts the chances of getting a job.
You might find it helpful to look at a couple of answers I wrote for similar questions a little while ago: http://relationships.blurtit.com/4265804/discuss-the-factors-that-cause-or-influence-teenagers-to-engage-in-types-of-risky and http://health.blurtit.com/4266192/what-is-the-impact-of-risky-behaviour. I thought the answer to this question was quite good too: http://science.blurtit.com/3152741/describe-the-impact-of-risk-behaviour.
Additionally, you might want to take a look at this video I found on YouTube:
It's an hour long though, so you might just want to skip through it to find the most relevant parts to your question.
Changes in Youth Risk behavior
Define the concept of risk behavior and explain why it is important for teenagers to investigate and be knowledgeable about it