Fifteen years ago teenagers were riding BMX bikes, listening to Boy George, and their major health worries were periods and pimples.

But two doctors who wrote a best-selling health guide for teens in 1987 have had to give their books a revamp to bring them up to date.

Their first editions barely mentioned drug abuse, bullying and the sexually-transmitted disease chlamydia. But these are major topics discussed in depth in the up-dated versions of The Diary of a Teenage Health Freak and its companion for girls The Diary of the Other Health Freak.

Back in 1987 Aids was the issue of the day, and the importance of practising safe sex was the dominant theme. Gay sex was pretty much a taboo subject with teenagers in the days before the age of consent was lowered from 21 to 18 for male homosexuals, and hardly got a mention.

The first edition was also published in the days before the phenomenon of ecstasy - drug abuse took up just a small section.

Co-author Dr Ann McPherson said chlamydia was not referred to in her first book but is now given prominence in its chapters focusing on sexual health.

It is a reflection of the fact that chlamydia cases have doubled in six years as a new generation of young people who missed out on the Aids scare of the 1980s failed to practise safe sex, she said.

The latest research suggests that chlamydia is responsible for nearly a third of all infertility cases, and confirms that many victims do not realise they have it until it is too late.

Dr McPherson said: “There are all sorts of things that have happened in the world to change teenage life such as the Internet, mobile phones and texting.

“We know that more teenagers are being offered drugs and trying them. We felt we had to address it and put it into the context of what is really dangerous.

“It was the same with sex. A lot of information regarding emergency contraception is different. If all teenagers who took a chance took the morning-after pill the abortion rate would reduce by 70 per cent.

“But the book does take quite a moral tone. We point out the latest research which says that a lot of teenagers who have had sex too early go on to regret it.”

Sexual orientation is another issue given more information as “it is now more acceptable to talk about being gay with teenagers”.

The books have sold 750,000 copies worldwide and have been translated into 22 languages. They provided the model for the Channel 4 television programme Teenage Health Freak.

Two series of six programmes were made in the late 1980s in which Blackadder star Tony Robinson played the headteacher.

The books deal with issues through the eyes of the fictional Peter Payne, the “terminal teenage hypochondriac”, and his sister Susie. They cover the major personal, social and health education curriculum in key stages 3 and 4 and many of the citizenship issues such as bullying, racism and the environment.

Dr McPherson and co-author Dr Aidan Macfarlane have also set up an award-winning website - www.teenagehealthfreak.org - which receives around 190,000 hits a week.

‘The Diary of a Teenage Health Freak’ and ‘The Diary of the other Health Freak’ by Dr Ann McPherson and Dr Aidan Macfarlane will be published on April 8 by Oxford University Press, pound;4.99 each