Antibiotics seem to increase the risk of developing fibromyalgia up to four-fold, according to a case-control study of data from UK primary care.

Researchers matched 44,674 people with fibromyalgia to 133,513 controls. Ninety per cent of participants were female and the average age was 46 years. Allowing for confounders, antibiotics doubled the likelihood of developing fibromyalgia. Each antibiotic prescription increased fibromyalgia risk by 11 per cent.

The volume and timing of antibiotic prescriptions influenced the risk of being diagnosed with fibromyalgia. The quartile with the highest number of prescriptions were almost four times more likely to develop fibromyalgia (OR 3.92) than controls. The quartile with the longest exposure were about three times (OR 3.28) more likely to develop fibromyalgia. 

The risk seemed especially high with certain antibiotics, including metronidazole (OR 2.24), tetracyclines (2.07) and those used to treat UTIs (OR 1.95). In general, prescriptions issued closer to the diagnosis had the strongest association with fibromyalgia: increases of 2.72 and 1.94 two years and more than 10 years respectively after their most recent antibiotic prescription.

The composition of the GI microbiome seems to influence pain perception by modulating the gut-brain axis. The authors of the study point out that fibromyalgia and IBS are closely associated which, they suggest, supports “a common aetiological pathway … given the known relationship between [fibromyalgia] and IBS, the altered gut microbiome of the latter may also be implicated in the former”. 

Alternatively, antibiotic consumption may indicate recurrent infections. Lowered immunity may trigger fibromyalgia. While the mechanisms need further investigation, antibiotics may be “an important risk factor”, the authors say.