Any potential benefits of the antidepressant mirtazapine in fibromyalgia are outweighed by its potential harms, a Cochrane review concludes.

The review of three studies involving 606 participants comparing mirtazapine with placebo showed no benefit of mirtazapine over placebo for pain relief of 50% or greater, Patient Global Impression of Change, improvement of HRQoL of 20% or greater, or reduction of fatigue or negative mood.

Clinically‐relevant benefits were shown for some secondary outcomes – patient reported pain relief of 30% or greater (number needed to treat = 8 for an additional beneficial outcome), reduction of mean pain intensity, and sleep problems.

However clinically relevant side effects such as somnolence (42% vs 14%; number needed to harm n=5), weight gain (19% versus 1%; number needed to harm n=6), and elevated alanine aminotransferase (3% versus 2%; number needed to harm n=8) were more frequent with mirtazapine than placebo.

The review by the Cochrane Pain, Palliative and Supportive Care Group noted that overall the quality of evidence was low or very low, with two of the three studies of questionable quality. 

“On balance, any potential benefits of mirtazapine in fibromyalgia were outweighed by its potential harms, though, a small minority of people with fibromyalgia might experience substantial symptom relief without clinically‐relevant adverse event,” they concluded.

Mirtazapine is not approved for fibromyalgia in any country.