Parents of teenagers feel like failures and are worried they are raising a generation of "monsters", a study reveals.
They feel they have little or no influence over their children, and are unable to cope with binge drinking, drug-taking and early sexual activity among young people.
The study, by the support group Parentline Plus, found that many parents were shocked by the changes in their children as they entered adolescence.
An analysis of the 50,000 calls to the organisation last year found that more than four out of 10 reported conflict with teenagers. More than 82 per cent of parents worried about early sexual activity, particularly among 13 to 15-year-old girls.
Binge-drinking was another worry among parents of girls, who feared their daughters losing control and having unprotected sex.
The mother of a former competitive gymnast, now 14, said: "She has developed into a desperate teenager. She has tried drinking and now says she smokes and can't stop.
"I am terrified she may want to try sex. I want my little girl back, not this troublesome teenager on a mission to catch up on what she may have missed while she trained."
Drug use also scared parents, the study found, because they did not understand the risks or the on-going debate about legalising cannabis.
Calls about drug misuse were mainly about boys, and almost a third said their sons had stolen to feed their habit and lied about it.
The charity set up a separate survey on its website called "Parenting Teenagers, the highs and lows", between December 2005 and January 2006, completed by a total of 155 parents.
The aim was to give them the chance to recount their own experiences about what life was like living with a teenager.
One father said he had to ground his daughter. "Only last week she was found drunk in the park with her boyfriend and was rushed to hospital to have her stomach pumped," he wrote.
"She also has an eating disorder and I found a powder substance in her jacket pocket."
Another said: "My eldest daughter has changed from a loving girl into a monster.
"You cannot communicate with her because everything I say she takes as a personal attack and tells me I'm ruining her life."
Parents often blamed themselves for their teenagers' behaviour and believed they were out of touch and unable to give the right advice and information to their children.
Dorit Braun, the charity's chief executive said most families survived the traumas of adolescence and their relationships were unaffected in the long term. But she said: "The challenge to policy-makers, commissioners and providers, is to deliver a flexible and appropriate support service, backed by adequate and long term investment, which breaks through the isolation experienced by parents of teenagers."
www.parentlineplus.org.uk. Free 24-hour helpline, 0808 8002222
Just never give up Chris Jubb took a course of parenting classes as his six children were growing up.
"I didn't really believe I needed lessons but a friend who was running them encouraged me to go along as he wanted to attract more men," he said. "I didn't realise until later how useful they would be."
Mr Jubb, and his wife Carol, both 50, know all about teenagers. Their children - four boys and two girls - are aged from 22 to 12 and so far each child has dealt with adolescence differently. "My eldest was very independent and ended up travelling around the world at 16. Another seemed upset for much of the time, while a third was very individual, acted tough and didn't want to carry on at school. It got to a stage where he wasn't even fitting into the family very well. At times I felt like throwing him out but I'm glad I never did."
Mr Jubb, whose family live in Tooting, south London, believes adults should not be afraid of initiating discussions with children about difficult subjects.
"I got through to one of my children through a process called reflective listening, which I picked up in the classes," he said.
"It means you continue a conversation with a child even when they give one-word answers and are reluctant. Eventually it makes them feel connected to you as a parent and they start to open up more. It means that the parent has to concentrate on that discussion."
He said the important thing about parenting was perseverance. "You must never give up, and this is an important aspect of getting though those teenage years," he said.