Serotonin and noradrenaline reuptake inhibitors for fibromyalgia

Researchers in the Cochrane Collaboration conducted a review of research about the effects of serotonin and noradrenaline reuptake inhibitors (SNRIs) on fibromyalgia syndrome (FMS). After searching for all relevant studies, they found 10 studies with up to 6038 people. Their findings are summarized below.

Adults with FMS, who took the SNRIs duloxetine or milnacipran rather than a fake medication (placebo), were likely to have :

- reduced pain,

- slightly improved quality of life and reduced fatigue,

- no improvement for sleep problems,

- more drug-induced side effects and a greater likelihood of stopping medication.

Serious side effects such as liver damage and suicidality were very rare. There was no difference between the SNRIs duloxetine or milnacipran and fake medication for these serious side effects.

What is fibromyalgia syndrome and what are serotonin and noradrenaline reuptake inhibitors?

People with FMS suffer from chronic widespread pain, sleep problems and fatigue. There is no cure for FMS at present, so the treatments aim to relieve the symptoms and to improve quality of life.

Serotonin and noradrenaline are chemicals which are produced by the human body, involved in the regulation of pain, sleep and mood. Low concentrations of serotonin have been reported in people with FMS. SNRIs are antidepressants that increase the concentration of serotonin and noradrenaline in the brain.

The SNRIs duloxetine and milnacipran had been approved by the US Food and Drug Administration but not by the European Medicines Agency for the management of FMS. The US and European Regulatory Authorities differed in their judgment of the efficacy and safety of both drugs. Therefore it is important to know for people with FMS and healthcare providers on the effects of SNRIs on FMS.

Best estimate of what happens to people with FMS when they take duloxetine or milnacipran after an average of 18 weeks


Pain was reduced by 50% in:

- 29 out of 100 people taking duloxetine or milnacipran

- 19 out of 100 people taking placebo.

- Therefore, 10 more people in every 100 benefited from duloxetine or milnacipran than benefited from placebo (10% absolute improvement).

Sleep problems and fatigue:

People taking duloxetine or milnacipran reported a slight reduction in fatigue and the same amount of sleep problems as people taking placebo.

Disease-related quality of life (QOL):

- People taking duloxetine or milnacipran scored their quality of life as 14 (on a scale of 0 to100),

- People taking placebo scored theirs as 10. 

- This means that people taking duloxetine or milnacipran rated their quality of life four points higher than people taking placebo.

Stopping treatment due to the side effects:

- 20 people out of 100 taking duloxetine or milnacipran stopped medication due to side effects.

- 11 people out of 100 taking fake medication stopped medication due to side effects.

- This means that 9 more people out of 100 stopped taking duloxetin or milnacipran than stopped taking fake medication because of side effects.

Serious adverse events:

There were no differences between duloxetine or milnacipran and fake medication in the number of serious adverse events.

We often do not have precise information about side effects and complications. This is particularly true for rare but serious side effects. Possible side effects may include nausea, dry mouth, headache, constipation and hyperhidrosis. Rare complications may include suicidality, liver damage, abnormal bleeding, elevated blood pressure and urinary hesitation.

Authors' conclusions: 

The SNRIs duloxetine and milnacipran provided a small incremental benefit over placebo in reducing pain. The superiority of duloxetine and milnacipran over placebo in reducing fatigue and limitations of QOL was not substantial. Duloxetine and milnacipran were not superior to placebo in reducing sleep problems. The dropout rates due to adverse events were higher for duloxetine and milnacipran than for placebo. The most frequently reported symptoms leading to stopping medication were nausea, dry mouth, constipation, headache, somnolence/dizziness and insomnia. Rare complications of both drugs may include suicidality, liver damage, abnormal bleeding, elevated blood pressure and urinary hesitation.

Read the full abstract...

Fibromyalgia syndrome (FMS) is a clinically well-defined chronic condition of unknown etiology characterized by chronic widespread pain that often co-exists with sleep disturbances, cognitive dysfunction and fatigue. Patients often report high disability levels and poor quality of life (QOL). Drug therapy focuses on reducing key symptoms and improving quality of life.


To assess the benefits and harms of serotonin and noradrenaline reuptake inhibitors (SNRIs) compared with placebo for treating FMS symptoms in adults.

Search strategy: 

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), (The Cochrane Library 2012, Issue 9), MEDLINE (1966 to September 2012), EMBASE (1980 to September 2012), (U.S.-marketed pharmaceuticals) (to September 2012) and (to September 2012) for published and ongoing trials and examined the reference lists of reviewed articles.

Selection criteria: 

We selected randomized, controlled trials of any formulation of SNRIs against placebo for the treatment of FMS in adults.

Data collection and analysis: 

Two review authors independently extracted the data from the included studies, and assessed the risks of bias of the studies. Discrepancies were resolved by discussion.

Main results: 

Ten studies were included with a total of 6038 participants. Five studies investigated duloxetine against placebo, and five investigated milnacipran against placebo. A total of 3611 participants were included into duloxetine or milnacipran groups and 2427 participants into placebo groups. The studies had a low risk of bias in general. Duloxetine and milnacipran had a small incremental effect over placebo in reducing pain (standardized mean difference (SMD) -0.23; 95% confidence interval (CI) -0.29 to -0.18; 6.1% relative improvement). One-hundred and ninety-two participants per 1000 on placebo reported an at least 50% pain reduction compared to 280 per 1000 on SNRIs (Risk ratio (RR) 1.49, 95% CI 1.35 to 1.64; number needed to treat to benefit (NNTB) 11, 95% CI 9 to 15). Duloxetine and milnacipran did not reduce fatigue substantially (SMD -0.14; 95% CI -0.19 to -0.08; 2.5% relative improvement; NNTB 17, 95% CI 12 to 29), and did not improve QOL substantially (SMD -0.20; 95% CI -0.25 to -0.14; 4.6% relative improvement; NNTB 12, 95% CI 9 to 17) compared to placebo. There were no statistically significant differences between either duloxetine or milnacipran and placebo in reducing sleep problems (SMD -0.07; 95% CI -0.16 to 0.03; 2.5% relative improvement). One-hundred and seven participants per 1000 on placebo dropped out due to adverse events compared to 196 per 1000 on SNRIs. The dropout rate due to adverse events in the duloxetine and milnacipran groups was statistically significantly higher than in placebo groups (RR 1.83, 95% CI 1.53 to 2.18; number needed to treat to harm (NNTH) 11, 95% CI 9 to 13). There was no statistically significant difference in serious adverse events between either duloxetine or milnacipran and placebo (RR 0.78, 95% CI 0.55 to 1.12).