Pain intensity rating as an assessment tool at crossroads in the clinic and in clinical research

Pain Management Clinical Trials, Opiod, Clinical Trials, Clinical Research
numeric pain rating scale


Pain intensity rating, most often administered as a numeric pain rating scale (NPRS), where 0 is no pain and 10 is the worst pain imaginable, has been an essential pain assessment tool in clinical research for decades and in everyday clinical practice for more than a decade and a half when it was introduced as a Fifth Vital Sign.

In clinical practice, it has been a standard and a mandate that clinicians assess pain as a Fifth Vital Sign and also to intervene with the goal to lessen severe pain in their patients. The wide acceptance of the standard to assess severe pain and to respond with the simplest intervention of prescribing analgesics resulted in overprescribing.

numeric pain rating scale

Unfortunately, standards in prescribing opioids have not been based on solid science when it comes to long term efficacy. This failure is combined with the lack of even basic standards in assessing pain in clinical trials, beyond pain intensity ratings, such as assessment of side effects of analgesics and patient function. The impact extends to the larger medical community when it comes to prescribing opioids as advocated by professional pain societies. The outcome of overprescribing of opioids is that the medical community and society at large are facing an epidemic of opioid overdose deaths. In response to the call to act in response to this situation, clinicians in primary care are reassessing the approach of using pain ratings as the Fifth Vital Sign.1

Numeric Pain Rating Scale Blamed in Part for High Failure Rate of Pain Clinical Trials

In clinical research this pain assessment tool has been viewed as too crude, imprecise and nonspecific to assess complexity of pain2 as a research subject on one hand and as insensitive to change when therapies are administered. This property of NPRS was blamed in part as one of the reasons for the astronomical failure rate of pain clinical trials. Many approaches were considered by investigators and sponsors of pain management trials with the goal to explore secondary outcome measures. But for the majority of trials, one form or the other of NPRS-based outcome is still the primary outcome in analgesic studies.

To tackle the issue of imprecision of NPRS and other related issues, recently the FDA has taken a step to ameliorate this concern by supporting a study to establish a more appropriate pain rating tool or an outcome measure in acute and chronic pain trials. Unfortunately, in the absence of any other tool to replace that function for the time being, some form of NPRS is here to stay in spite of its limitations. 

Certainly, it is now up to professional pain societies to come together with pain clinical and research communities and to engage in a dialog about how to develop a pain assessment tool or tools that would reflect the complex nature of pain on one hand and versatility and ease of use in a wide range of settings where pain assessment is critical. The stakes are high and a successful outcome of this effort should aid in advancing pain research and pain care, and certainly facilitate development of new analgesic therapeutics.

Our Approach to Pain Management and Analgesics Development Trials

For further information about assessment tools we leverage in pain clinical trials, please contact Worldwide Clinical Trials at +1 610-964-2000 or visit


  1. Many Physicians, Nurses Want Pain Removed as Fifth Vital Sign by Alicia Ault Medscape Survey, February 21, 2017
  2. Williams A, Davies HTO, Chadury Y . Simple pain rating scales hide complex idiosyncratic meanings. Pain, 85, 457 – 463. 2000

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