Infertility treatment could exacerbate disease in multiple sclerosis (MS), a new study suggests. 16 patients with relapsing–remitting MS were monitored for 12 months prior to 26 treatment cycles of gonadotropin-releasing hormone agonists and follicle-stimulating hormone and were followed up for 9 months. Compared with baseline, treatment was associated with a sevenfold increased risk of disease exacerbation and a ninefold increased risk of enhanced MRI activity.