A bad back may be one of medicine's most perplexing ailments but there is no puzzle over the best way to cure it, doctors conclude today. A couple of paracetamol and a bit of reassurance from the GP is all that is needed to put sufferers back on their feet.

Strong painkillers or spinal manipulation – massage by a physiotherapist – make no difference to the speed of recovery, the researchers found.

Back pain is the third most common reason for consulting a doctor, after headaches and tiredness, but doctors often cannot find a specific cause. An estimated £1.6bn is spent on treating back pain in Britain each year and billions more is lost in days off work.

GPs are currently taught to reassure patients that they will get better and to advise them to keep active and avoid bed rest (which tends to make the condition worse), and to take a couple of paracetamol when required.

If that does not work they are advised to offer a stronger painkiller such as the anti-inflammatory drug diclofenac and spinal manipulation to speed up recovery.

Researchers who studied 240 patients with acute lower back pain found prescribing spinal manipulation and a stronger painkiller made no difference. They suggest that paying for the treatment – either by the patient or the NHS – is a waste of money.

The finding is another blow to the reputation of the "back crackers" – physiotherapists, osteopaths and chiropractors – whose professional raison d'etre is founded on their ability to cure bad backs. A series of studies has failed to show significant benefit from their treatments and called into question their value – findings which have angered organisations representing practitioners of spinal manipulation.

In the latest study, conducted in Australia, patients with acute back pain were divided into four groups. Those who had the basic advice to stay active and take paracetamol got better just as quickly as those who were given the basic advice plus the stronger painkiller and spinal manipulation. Writing in The Lancet, Mark Hancock and colleagues from the Back Pain Research Group at the University of Sydney, say: "Neither diclofenac nor spinal manipulative therapy gave clinically useful effects on the primary outcome of time to recovery.

"Findings from the secondary analyses support the primary analyses, showing no significant effects on pain, disability or global perceived effect at one, two, four or 12 weeks when diclofenac or spinal manipulative therapy or both were added to baseline care."

They add that spinal manipulation and powerful painkillers carry risks, and both are expensive, so patients and the NHS will be better off without them.

A spokesman for the General Chiropractic Council said: "Spinal manipulation is part of a package of care offered by chiropractors including lifestyle and posture advice, rehabilitation and specific exercises. The study did not address chiropractic techniques."

How to avoid back pain

* Do gentle stretching while still in bed

* Get regular exercise – walk to work, climb stairs

* Shift position when driving or watching TV

* Take frequent breaks from your desk

* Build up strength

* Don't get overweight; give up smoking

* Check mattress and pillows provide support

* Maintain good posture and ensure your chair has good back support

* Keep back stiff and bend knees when lifting, and never carry heavy loads