Ibuprofen is commonly used to treat knee pain
Gels or creams containing painkillers are better than tablets for chronic knee pain, NHS research suggests.
A study of almost 600 patients aged over 50 found the anti-inflammatory creams worked as well as the oral versions and had fewer side-effects.
And although they cost more initially, topical treatments may save the NHS money in the long run, the Queen Mary University of London researchers said.
It is estimated that a third of over 50s suffer from knee pain.
In half of those the problem is classed as severe.
The most common cause of pain in the knee is osteoarthritis - a condition caused by abnormal wearing of the cartilage.
A total of 585 patients from 26 general practices around the UK took part in the study which looked specifically at non-steroidal anti-inflammatories (NSAIDs) - a class of drugs which includes ibuprofen.
Both tablets and creams containing the drugs had the same effect on knee pain, the study showed.
But those treated with oral medication had more minor adverse effects such as indigestion, increased blood pressure, or worsening asthma.
NSAIDs are well-known to be associated with sometimes serious side effects but the topical preparations deliver a smaller dose directly to the affected area and so are less likely to cause such problems.
Patients also preferred the gels and creams, the study which is published on the National Institute for Health Research website.
Study leader Professor Martin Underwood, who has since moved to Warwick University, said there had been uncertainty about which to use.
"There has been quite a lot of discouragement about using topical NSAIDs because it was thought they were more expensive and there was not good evidence they were beneficial."
He added that patients with more widespread pain may find tablets are better and should discuss the choice with their GP.
Royal College of GPs chairman Professor Steve Field said he had always been of the view that oral NSAIDs worked better.
"This is an important message for GPs and patients - that they should consider topical treatments to avoid side effects."
An Arthritis Research Campaign spokeswoman said GPs had probably under-prescribed topical creams in the past because they did not believe they were as effective.
"But this new research appears to show they both as effective and safer, with fewer of the side affects associated with NSAID tablets," she added.