Antibiotics are used to treat many common ailments
Doctors in England and Wales are being told not to hand out antibiotics for common coughs and colds to help save the NHS millions of pounds a year.
The over-prescription of antibiotics has been linked to the development of "superbugs" that resist treatment.
Some 38m prescriptions for antibiotics were written by doctors in the UK in 2007, costing the NHS £175m.
The National Institute for Health and Clinical (Nice) says the drugs do little to help cure coughs and colds.
Many are caused by viruses, which do not respond to antibiotics.
Figures show that a quarter of people in England and Wales visit their GP every year because of symptoms of a respiratory tract infection, which accounts for 60% of all antibiotic prescribing in general practice.
But guidelines published by Nice say doctors should defer from prescribing antibiotics straight away for ear infections, sore throats, sinus trouble and coughs and colds in children and adults.
It also gives guidance on when to prescribe the drugs, including issuing a prescription for use later on should the symptoms worsen.
Doctors have been told before to desist from prescribing antibiotics for coughs and colds, but there is concern that rates are still too high.
Dr Gillian Leng, deputy chief executive of Nice, said: "This is the first practical guideline which will help all healthcare professionals to assess adults and children with respiratory tract infections to decide whether their condition will improve by taking antibiotics.
"The guidance will also ensure that they can be followed up by the right people, at the right time and within the right healthcare setting."
Mike Sharland, consultant paediatrician and guideline development group member, said: "Every year, over five million antibiotics are prescribed for children in the community - the great majority for upper respiratory tract infections, which are nearly always viral."