The Study Was a Success. But Not for People Like You.
Clinical trials for pain medication often work. In the carefully selected group of patients enrolled, the treatment shows benefit. The drug gets approved.
Then doctors start prescribing it to their actual patients — who have depression, or take other medications, or have multiple health conditions — and the results are far less impressive.
Why? Because those patients were excluded from the trial in the first place.
Nerve Pain Is Already Difficult Enough
Neuropathic pain — nerve pain — affects roughly 7-10% of the general population. It's the burning, shooting, or electric-shock sensation that comes from nerve damage or malfunction. It can be caused by diabetes, shingles, chemotherapy, spinal injury, or dozens of other conditions.
It is notoriously hard to treat. Most available medications work for fewer than half of patients. And the patients who struggle most to get relief are often those with additional conditions — anxiety, depression, multiple medications.
Old Approach vs. What This Review Revealed
Clinical trials use exclusion criteria to keep study populations clean and manageable. That makes sense for isolating a drug's effect. But the practice can go too far.
But here's the twist: this analysis found that psychological conditions were excluded from more than half of neuropathic pain trials — even though depression and anxiety occur alongside chronic pain in a very large share of real patients.
Why Exclusion Criteria Matter So Much
Think of a clinical trial like a recipe test in a professional kitchen — controlled conditions, premium ingredients, experienced chefs. But most people are cooking at home, with what's in the fridge, under stress.
When a drug is tested only in the professional kitchen, you don't know how it will perform in real life. The more patients you exclude from the trial, the wider that gap becomes.
Researchers systematically reviewed 161 published clinical trials of treatments for neuropathic pain, all published between 2012 and 2022. They catalogued every exclusion criterion listed in each trial and analyzed which types of patients were most commonly excluded and why.
The median trial used five exclusion criteria (with a range that extended much higher). Medical conditions were the most common exclusion, used in 86% of trials. Age restrictions were applied in 71% of trials. Minimum pain score requirements — meaning patients whose pain wasn't severe enough to be enrolled — were used in 72% of trials.
But the most striking finding was this: psychological comorbidities were excluded in nearly 57% of trials. Depression and anxiety are among the most common conditions to co-occur with chronic pain. Excluding them from trials creates a research population that looks nothing like the patient population seeing doctors every day.
That's Not the Full Story
Only 36% of trials even reported how many patients were screened — making it impossible to know how many people were turned away.
Without that information, there's no way to assess whether the enrolled patients were representative or an unusual subset. Transparency in research reporting has a real cost when it's missing.
When patients receive a medication for nerve pain and it doesn't work, one explanation is that they're in the group that was never studied. Doctors may assume the drug failed for this patient specifically — when actually, the drug was never designed or tested for people like them.
This has downstream effects on prescribing, on patient trust, and on the healthcare system as a whole. Patients who cycle through ineffective treatments lose faith in medicine. Doctors spend time managing side effects of drugs that had little chance of working for that population.
If you live with neuropathic pain and have depression, anxiety, or multiple health conditions, this research helps explain why finding effective treatment can feel especially frustrating. It doesn't mean treatments can't work for you — but it does mean the evidence base is thinner.
When talking to your doctor about pain treatment options, it's reasonable to ask whether the evidence behind a recommended medication included patients with your full range of conditions. If not, framing the treatment as a carefully monitored trial — with a plan to reassess — is a reasonable approach.
This analysis only reviewed 161 trials from a 10-year window and focused specifically on neuropathic pain. Other chronic pain conditions may look different. The review also couldn't assess whether the exclusion criteria used were medically necessary or simply habitual — that's a harder question to answer from published data alone.
What Comes Next
The study authors recommend standardizing how exclusion criteria are reported and requiring trials to document how many patients were screened and why they were excluded. Some research funders are already pushing for more "pragmatic" trial designs that include broader, more representative populations. If that shift takes hold, the next generation of pain research could produce results that are far more useful to the patients who need them most.