Multiple sclerosis requires long-term management, often with disease-modifying therapies. Poor medication adherence, especially to injectables, can increase relapse and hospitalisation rates and consume healthcare resources. We discuss adherence definitions and terminology and its prevalence in multiple sclerosis (MS). Typical causes of poor adherence in patients with MS include: insufficient efficacy or tolerability, concurrent disorders, and consequences of MS (e.g., forgetfulness, depression, fatigue and poor motor skills). Ways to improve adherence rates are reviewed, focusing on interdisciplinary healthcare teams, good communication between healthcare workers and patients (and their families), ongoing support and digital tools to promote adherence. We consider open communication and continuing education to be key, and that MS nurses have a pivotal role in ensuring patients' adherence to MS medicines.