Sports scientists say paracetamol, ibuprofen and other painkillers may trick athletes’ bodies into working harder, resulting in higher performance.
Over-the-counter drugs are routinely used by about one in three elite competitors to speed recovery, ease pain and boost endurance, but researchers fear long-term use could cause asthma and carry other significant health risks.
Pills may also allow athletes to train with greater power and intensity because they reduce pain thresholds and feelings of effort while exercising.
Daniel Awde told the BBC that it's a 'running joke' athletes take ibuprofen 'for breakfast, lunch and dinner' as scientists say they may give competitors an unfair advantage
A review suggests the drugs may be give an unfair advantage to users by subduing the brain structures that otherwise tell them they are exercising too hard, according to The Times.
One survey found over 90 per cent of Italy's professional footballers had taken anti-inflammatory painkillers including ibuprofen and aspirin.
Others suggest over 20 per cent the athletes competing in 2000's Olympic Games in Sydney used the drugs, with 10 per cent taking them at the 2004 Athens Games.
Former England rugby union captain Lewis Moody accused fellow players of competing to see how many analgesics they could take.
And Olympic decathlete and 400 metre runner Daniel Awde said it was a 'running joke' that athletes take ibuprofen 'for breakfast, lunch and dinner' in a BBC documentary.
Lewis Moody accused fellow rugby players of seeing how many analgesics they could take
Researchers at the University of Granada in Spain conducted several experiments, which showed small doses strengthen athletes, despite them usually taking the pills to manage injuries.
And a UK study in 2009 found that cyclists given 1.5g of paracetamol - about three tablets - finished 10-mile time-trial about 30 seconds faster than those on a placebo.
Separate sprint tests showed the same amount of paracetamol increased runners’ average power output by 5 per cent.
Two other papers also found the painkiller let participants to run for considerably longer in the heat.
Paracetamol's effects on the body are still not fully understood by scientists, despite the drug being used in Britain since 1956.
Athletes taking painkillers may be given an advantage as the drugs can inhibit signals that tell the body it is working too hard
But Darias Holgado, who was the lead author on the University of Granada research, believes there is evidence its effects go beyond easing pain.
'[It] could be that paracetamol might reduce the thermal stress experienced during exercise, and hence it may increase exercise capacity in hot conditions where body temperature plays an important role.
'Paracetamol might also reduce the brain output required to recruit the locomotor muscles for a given exercise intensity, lowering the perception of effort and making exercise feel easier — or for allowing more muscle-force production for the same level of perceived exertion.'
There is also weaker evidence of the performance-enhancing powers of ibuprofen and other anti-inflammatories.
But most experiments have been small, involving ordinary people as opposed to top-level athletes.
It's also possible that studies showing no effect remain unpublished in what researchers refer to as the 'file-drawer' problem.
Dr Holgado and his team haven't called for a ban, but said health complications and side-effects should be considered by all users after the review was published in American Academy of Physical Medicine and Rehabilitation journal PM&R.
'Athletes, medical staff and doping authorities should bear in mind the common side-effects and health complications associated with prolonged or supertherapeutic doses.'