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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).
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.
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
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.