Low back pain (LBP) occurs in many patients with fibromyalgia (FM). The current study aimed to assess the possible pain and function amelioration associated with medical cannabis therapy (MCT) in this setting. 31 patients were involved in an observational cross-over study. The patients were screened, treated with 3 months of standardised analgesic therapy (SAT): 5 mg of oxycodone hydrochloride equivalent to 4.5 mg oxycodone and 2.5 mg naloxone hydrochloride twice a day and duloxetine 30 mg once a day. Following 3 months of this therapy, the patients could opt for MCT and were treated for a minimum of 6 months. Patient reported outcomes (PRO's) included: FIQR, VAS, ODI and SF-12 and lumbar range of motion (ROM) was recorded using the modified Schober test. While SAT led to minor improvement as compared with baseline status, the addition of MCT allowed a significantly higher improvement in all PRO's at 3 months after initiation of MCT and the improvement was maintained at 6 months. ROM improved after 3 months of MCT and continued to improve at 6 months. This observational cross-over study demonstrates an advantage of MCT in FM patients with LBP as compared with SAT. Further randomised clinical trial studies should assess whether these results can be generalised to the FM population at large.