Evidence
Alert

Gabapentin does not reduce long-term pelvic pain, and has unpleasant side effects, research finds

Gabapentin should not be used to treat women with long-term (chronic) pelvic pain. New research found that the drug does not reduce pain, nor does it improve women’s physical and emotional wellbeing. Compared to a dummy pill (placebo), gabapentin was also linked to serious side effects.

More than one million women in the UK have chronic pelvic pain. For some, this long-lasting pain can be linked to conditions such as endometriosis but for over half these women, there is no apparent cause. It affects their quality of life, their physical wellbeing, sex life, family and social life. 

Gabapentin appears to ease nerve pain in conditions such as diabetes and shingles. Increasingly, in the absence of proven treatments, GPs and gynaecologists are prescribing this drug for chronic pelvic pain. It is linked to side effects such as sleepiness, drowsiness and, more rarely, more serious side effects such as suicidal thoughts. In some cases, it can be addictive

The study found that gabapentin did not reduce chronic pelvic pain and recommends that it should not be used for women with no obvious cause for their pain. Researchers say the women should be advised that the drug has unpleasant side effects and may not relieve their pain. 

What’s the issue?

Chronic pelvic pain affects around one in six women and is the reason for one in five gynaecological consultations. It causes intermittent or constant pain in the lower abdomen over a long period of time. It is more intense than the pain associated with periods and lasts longer. Women commonly report a significant impact on their physical wellbeing, sex life, work, and social life.

Sometimes the pain is linked to specific conditions, such as endometriosis (in which tissue similar to the lining of the womb grows elsewhere in the pelvis). But for over half of women, no underlying cause for the pain can be found. There are no proven treatments to reduce chronic pelvic pain. An effective treatment would greatly improve these women’s quality of life and may avoid a repeating cycle of referrals, investigations, and operations

Gabapentin is used to treat other chronic pain conditions such as fibromyalgia (in which people may have pain all over their body). Because of this, the drug is increasingly prescribed for chronic pelvic pain. In two separate surveys, three-quarters of GPs and nine in ten gynaecologists said that they would consider prescribing gabapentin for chronic pelvic pain. However, it is not licensed for this use in the UK and evidence to support its effectiveness is lacking.

Researchers wanted to find out whether gabapentin was able to reduce pain and improve the lives of women with unexplained chronic pelvic pain. This is the first large trial comparing gabapentin with a dummy pill (placebo). 

What’s new?

The GaPP2 study was designed with support from the patient organisation, Pelvic Pain Support Network. It involved around 300 women with unexplained chronic pelvic pain, who were being treated in 39 different UK hospitals. Half the women received gabapentin and the other half a placebo for 16 weeks. Neither the women nor the clinicians who dispensed the medication knew which they were receiving. 

The women rated their average pain and worst pain, using a scale from zero to ten, on a weekly basis. They also gave information about their physical and emotional wellbeing, fatigue, sexual activity and work productivity at the beginning and end of the study.

Gabapentin did not reduce pain and did not improve any other aspects of women’s lives. 

At the end of the trial:

    • the average worst pain scores were similar in both groups (7.1 with gabapentin; 7.4 with placebo)
    • the average pain scores were also similar (4.3 with gabapentin; 4.5 with placebo)
    • side effects such as dizziness, drowsiness and changes in mood were much more common with gabapentin than placebo.

Why is this important?

The findings of the GaPP2 study conclude that gabapentin should no longer be given to treat unexplained chronic pelvic pain. 

Women with no obvious underlying cause need to know that gabapentin will not ease their pain and may give them unpleasant side effects. If a woman is already taking gabapentin and decides to stop, she needs to discuss this with her doctor. Women need to gradually reduce their dose before stopping completely.

What’s next?

As a result of this study, the Royal College of Obstetricians and Gynaecologists (RCOG) will update its existing guideline for pelvic pain. 

A member of the research team is keen to explore the effectiveness of gabapentin for women who experience chronic pelvic pain alongside endometriosis. She is currently seeking funding.

The researchers suggest there is a value in exploring other avenues of treatment for chronic pelvic pain, such as different drugs, physiotherapy, and cognitive behavioural therapy. Clinical trials are needed to investigate this. 

A small subgroup of women in the GaPP2 study did respond to gabapentin. These women showed more activity than others on a brain scan (in a region of the brain called the anterior cingulate cortex) in response to the mild pain of a pinprick. However, this is a research finding which is unlikely to influence clinical practice, since it would require a costly brain scan to identify women who might benefit.

You may be interested to read

The full paper: Hewitt CA, and others. Gabapentin for chronic pelvic pain in women (GaPP2): a multicentre, randomised, double-blind, placebo-controlled trial. The Lancet 2020;396:10255 

The project report, including details of the sub-study which carried out brain scans in order to understand pain processing: Hewitt CA, and others. Gabapentin to reduce pain in women aged between 18 and 50 years with chronic pelvic pain: the GaPP2 RCT. Efficacy and Mechanism Evaluation 2020;7:7  

A video produced by the research team summarising the trial, the sub-study, their findings and the research to come.

The University of Edinburgh's Pelvic Pain team (EXPPECT) who who work to advance research into endometriosis and pelvic pain and their management.

The Pelvic Pain Support Network; a patient-led organisation offering support, information and advocacy for those living with with pelvic pain

The report on a study looking at whether it is possible to train staff to effectively deliver pelvic floor muscle training to women with pelvic organ prolapse: Maxwell M, and others. Pelvic floor muscle training for women with pelvic organ prolapse: the PROPEL realist evaluation. Health Services and Delivery Research 2020;8:47

 

Funding: This research was funded by the Efficacy and Mechanism Evaluation (EME) programme, a partnership between the NIHR and the Medical Research Council.

Conflicts of Interest: Two authors have received consultancy fees from various pharmaceutical companies. 

Disclaimer: NIHR Alerts are not a substitute for professional medical advice. They provide information about research which is funded or supported by the NIHR. Please note that views expressed in NIHR Alerts are those of the author(s) and reviewer(s) and not necessarily those of the NHS, the NIHR or the Department of Health and Social Care.

Commentaries

Study author

We polled the investigators and asked them if they thought gabapentin would work for these women. Everyone thought it would, because we prescribe it and we see it working. But the findings reveal that we could have prescribed a placebo and seen it work equally well. So, the results were really disappointing.

The good thing about showing it’s not effective is that gabapentin has side effects that can be worse than other drugs we might use, like antidepressants. It can be addictive, too, and enhance the effect of opiates. 

The guidelines on the use of this drug will soon be updated. We publicised the results and shared them on the website of the patient organisation the Pelvic Pain Support Network. So, I certainly hope it has been widely read by women with chronic pelvic pain.

Andrew Horne, Professor of Gynaecology and Reproductive Sciences, Medical Research Council Centre for Reproductive Health, Queen’s Medical Research Institute, University of Edinburgh 

Pelvic Pain Support Network  

I represented patients on this trial and also took gabapentin for a long period of time many years ago at treble the usual dose with no side effects but no benefit. At that time it was not monitored to see if it was helping. It has been in use for many years without proper trial evidence. There is very little in the way of medication to help people with long term pelvic pain. I would like to see similar rigorous trials on a couple more recent medications that are thought to be of greater benefit.  I found that two more recent medications in combination did help me.

Judy Birch, Co-Founder, Pelvic Pain Support Network

Clinician 

This study is well conducted and shows definitively that gabapentin should not be prescribed to women with chronic pelvic pain and no physical disease. Gabapentin is associated with significant side effects and more harm can be done by using this drug when there are no direct benefits.

Janesh Gupta, Professor of Obstetrics & Gynaecology, Birmingham Women’s Hospital