BACKGROUND: Chronic pelvic pain affects 2-24% of women worldwide and evidence 
for medical treatments is scarce. Gabapentin is effective in treating some 
chronic pain conditions. We aimed to measure the efficacy and safety of 
gabapentin in women with chronic pelvic pain and no obvious pelvic pathology.
METHODS: We performed a multicentre, randomised, double-blind, 
placebo-controlled randomised trial in 39 UK hospital centres. Eligible 
participants were women with chronic pelvic pain (with or without dysmenorrhoea 
or dyspareunia) of at least 3 months duration. Inclusion criteria were 18-50 
years of age, use or willingness to use contraception to avoid pregnancy, and no 
obvious pelvic pathology at laparoscopy, which must have taken place at least 2 
weeks before consent but less than 36 months previously. Participants were 
randomly assigned in a 1:1 ratio to receive gabapentin (titrated to a maximum 
dose of 2700 mg daily) or matching placebo for 16 weeks. The online 
randomisation system minimised allocations by presence or absence of 
dysmenorrhoea, psychological distress, current use of hormonal contraceptives, 
and hospital centre. The appearance, route, and administration of the assigned 
intervention were identical in both groups. Patients, clinicians, and research 
staff were unaware of the trial group assignments throughout the trial. 
Participants were unmasked once they had provided all outcome data at week 
16-17, or sooner if a serious adverse event requiring knowledge of the study 
drug occurred. The dual primary outcome measures were worst and average pain 
scores assessed separately on a numerical rating scale in weeks 13-16 after 
randomisation, in the intention-to-treat population. Self-reported adverse 
events were assessed according to intention-to-treat principles. This trial is 
registered with the ISRCTN registry, ISCRTN77451762.
FINDINGS: Participants were screened between Nov 30, 2015, and March 6, 2019, 
and 306 were randomly assigned (153 to gabapentin and 153 to placebo). There 
were no significant between-group differences in both worst and average 
numerical rating scale (NRS) pain scores at 13-16 weeks after randomisation. The 
mean worst NRS pain score was 7·1 (standard deviation [SD] 2·6) in the 
gabapentin group and 7·4 (SD 2·2) in the placebo group. Mean change from 
baseline was -1·4 (SD 2·3) in the gabapentin group and -1·2 (SD 2·1) in the 
placebo group (adjusted mean difference -0·20 [97·5% CI -0·81 to 0·42]; p=0·47). 
The mean average NRS pain score was 4·3 (SD 2·3) in the gabapentin group and 4·5 
(SD 2·2) in the placebo group. Mean change from baseline was -1·1 (SD 2·0) in 
the gabapentin group and -0·9 (SD 1·8) in the placebo group (adjusted mean 
difference -0·18 [97·5% CI -0·71 to 0·35]; p=0·45). More women had a serious 
adverse event in the gabapentin group than in the placebo group (10 [7%] of 153 
in the gabapentin group compared with 3 [2%] of 153 in the placebo group; 
p=0·04). Dizziness, drowsiness, and visual disturbances were more common in the 
gabapentin group.
INTERPRETATION: This study was adequately powered, but treatment with gabapentin 
did not result in significantly lower pain scores in women with chronic pelvic 
pain, and was associated with higher rates of side-effects than placebo. Given 
the increasing reports of abuse and evidence of potential harms associated with 
gabapentin use, it is important that clinicians consider alternative treatment 
options to off-label gabapentin for the management of chronic pelvic pain and no 
obvious pelvic pathology.
FUNDING: National Institute for Health Research.