95 placebo controlled studies were included in the review (n=5382 plus two studies where the number of patients was not stated). In addition data from four MAs were included, but the number of patients was not stated. The number of studies addressing the subgroups of pain were: six for acute pain, 13 for chronic low back pain, 28 for headache, one for chronic pelvic pain, two for pain associated with cancer, 13 for pain of osteoarthritis or rheumatoid arthritis, 12 for pain associated with fibrositis or fibromyalgia, two for facial pain, eight for ulcer healing, two for pain associated with irritable bowel syndrome and seven for pain of mixed aetiology.
Acute pain: 3 of 5 studies using S-NA drugs found the active treatment to be more effective than placebo. The one NA study found a positive treatment effect, whilst the one S study had a negative treatment effect.
Chronic low back pain: 8 of 10 S-NA trials found a positive treatment effect, as did 3 of 5 NA studies, whilst both S trials found a negative effect.
Headache: 15 of 18 S-NA trials found a positive treatment effect, as did 8 of 15 S trials and the one NA study.
Chronic pelvic pain: the one study which utilised a S antidepressant found a negative treatment effect.
Pain associated with cancer: of the two studies in this indication which both used a S-NA drug one gave positive and one gave a negative effect.
Oseoarthritic and rheumatoid arthritis: 7 or 11 S-NA trials found a positive treatment effect, as did half of the S trials (2 of 4). The one NA study reported a negative treatment effect. S-Adenosylmethionine (mechanism unknown) gave a positive effect.
Pain associated with fibrositis or fibromyalgia: All 10 S-NA studies reported a positive treatment effect, whilst 1 of 3 S studies reported a positive treatment effect. S-Adenosylmethionine (mechanism unknown) gave a positive effect.
Facial Pain: One trial with a S-NA and one with a S drug both found positive treatment effects. Ulcer healing: six of 8 trials that used a S-NA drug reported positive treatment effect. No other studies for this indication were included.
Pain associated with irritable bowel syndrome: Both studies, one with a S-NA and one with a NA antidepressant, reported positive treatment effects.
Pain of mixed aetiology: three of five S-NA trials found a positive treatment result, whilst one S trial found a positive, and one found a negative treatment effect.
The MA studies indicate that antidepressant drugs do have an anti-nociceptive effect, but because they pooled studies of different subgroups of antidepressants, they cannot provide information on the relative antinociceptive efficacy of the different subgroups.