For all the treatment modalities surveyed, only about half of treated patients had a response -- and the reduction in pain was only about 30%, reported Dennis C. Turk, MD, and colleagues from the University of Washington in Seattle.
"A general conclusion about the treatment of chronic noncancer pain is that the results presented are sobering," the researchers wrote in the June 25 Lancet.
Worldwide, one in five people report chronic pain, according to World Health Organization estimates.
Many factors influence patients' experience of pain, including cognitive and emotional elements, history, and pathology -- all of which need to be addressed for successful pain control.
To review the empirical evidence for common approaches to chronic pain, the researchers surveyed the literature for systematic reviews, meta-analyses, and guidelines on osteoarthritis, neuropathic pain, fibromyalgia, and low-back pain.
They found that opioids were the most commonly prescribed drugs, with sales that increased by more than 175% between 1997 and 2006 -- yet these agents were associated with only small improvements in pain and function.
In general, opioids were not recommended as first-line therapy for osteoarthritis and fibromyalgia, though they could be considered during specific clinical situations such as exacerbations of neuropathic pain.
Side effects such as constipation and drowsiness can be significant with opioids, and a small number of patients taking these drugs long term develop hyperalgesia.
Opioids also are widely misused, with studies suggesting that almost half of long-term users may be misusing the drugs and placing themselves at risk for overdose and death.
Other options include nonsteroidal anti-inflammatory drugs (NSAIDs), which can help in osteoarthritis and rheumatoid arthritis, although less is known about potential benefits for fibromyalgia or neuropathic pain.
Acetaminophen is widely used for analgesia as an alternative to NSAIDs, which can cause serious gastrointestinal adverse effects, but concern has been growing about toxicity and hepatic failure with acetaminophen and warnings have been added to the drug's labeling.
Antidepressant drugs, particularly the tricyclics, have various effects that could contribute to pain relief, such as interfering with the reuptake of noradrenaline and serotonin -- but these drugs can cause hypotension and arrhythmias.
Nonetheless, a recent systematic review determined that evidence for efficacy exists for the use of tricyclic antidepressants in several pain syndromes, including fibromyalgia and neuropathic pain.
The newer selective serotonin and noradrenaline reuptake inhibitors duloxetine (Cymbalta) and milnacipran (Savella) have been found effective in fibromyalgia and neuropathic pain, but more studies are needed to assess their effects in other conditions, according to Turk and colleagues.
Anticonvulsants also exert a number of actions that can interfere with pain, such as binding to a calcium-channel protein in the brain and spine, and inhibiting neurotransmitter release.
Studies have shown that gabapentin and pregabalin (Lyrica) are beneficial for neuropathic pain and fibromyalgia, although troublesome side effects include fatigue and weight gain.
Aside from pharmacotherapy, the researchers also reviewed several interventional approaches such as injections and surgery, finding some evidence for the use of epidural steroid injections in patients with radiculopathy associated with prolapsed lumbar discs.
A recent systematic review found some benefit for lumbar fusion for back pain, but many patients report worsening over time after the surgery.
"High complication rates and repeat procedures are realities of spinal surgery as well," the researchers observed.
Psychological techniques such as cognitive-behavioral therapy can have "modest benefits," they found, but long-term outcomes are uncertain, and individual patients may respond better to different types of psychological therapies.
Evidence also varies for complementary approaches, being "promising" for acupuncture in fibromyalgia.
Turk and colleagues noted that they would have liked to include a table summarizing their conclusions and comparing the various modalities, but were unable to do so because of the wide variety across studies in diagnostic criteria, outcome measures, and health systems.
They concluded that none of the widely used treatments are adequate for eliminating pain and improving function in most chronic pain patients.
They recommended that combinations of various types of treatment be evaluated, and also advised that helping patients maintain realistic expectations is vital.
In addition, they called for more clinical exploration into chronic pain.
"A great need exists for research that goes beyond asking the questions of whether a particular treatment is effective, to addressing what treatment is effective for which patients, on what outcomes, under what circumstances, and at what cost," they stated.