It sounds like the sort of treatment that can’t help but ease someone’s lower back pain: injecting corticosteroids directly into the epidural space of a patient’s spinal cord.

But a new review published in the Annals of Internal Medicine has concluded these epidural injections only offer mild, temporary relief for those suffering from a herniated disc and is no better than a placebo for those with spinal stenosis, or a narrowing of the spinal column that often results in lingering pain.

Analyzing thirty placebo-controlled clinical trials that studied people suffering from herniated discs, the authors found that there was an immediate improvement in pain, patient function, and short-term surgery risk for those given steroid injections over a placebo.

However, these improvements were “small and not sustained, and there was no effect on long-term surgery risk.” In the eight trials involving spinal stenosis, the authors found no clear difference between a placebo and epidural injection among the patients studied. And their findings didn’t indicate that any particular type of steroid or injection site resulted in better long-term outcomes. While the risk of severe side-effects remained low, the authors found that the reporting of adverse effects in the studies was fairly poor.

Though epidural injections are commonly used to alleviate lower back pain, there’s been a growing base of research showing that the treatment option is at best limited in its effectiveness. Another 2013 review published in the International Journal of Technology Assessment in Health Care concluded that epidural steroid injection therapies offered no long-term pain relief after six months, and weren’t any more useful at preventing later surgery than placebo or other treatments. And a March 2015 double-blinded and randomized study in The BMJ came to a similar conclusion when comparing the treatment to the anticonvulsant and painkiller gabapentin for people with lumbosacral radicular pain as a result of a herniated disc or spinal stenosis.

More worryingly, the authors of the 2013 review also found evidence of selection bias in the research they analyzed, indicating that researchers are tilting, perhaps inadvertently, the odds in favor of steroid injection, through the selection of patients included in their studies.

Of course, no one study, even a meta-analysis, should serve as the be-end, all-end of medical consensus. And the short-term relief brought on by steroid injections may still be a worthwhile avenue for patients to pursue, in conjunction with other treatments.

“I think the important thing is for patients and clinicians to be able to make informed decisions,” lead author Dr. Roger Chou of Oregon Health & Science University told Reuters Health . “Epidural corticosteroid injections are perceived as being more effective than they are.”

Source: Chou R, Hashimoto R, Friedly P, et al. Epidural Corticosteroid Injections for Radiculopathy and Spinal Stenosis: A Systematic Review and Meta-analysis. Annals of Internal Medicine. 2015.