Ocrevus (ocrelizumab) is a disease modifying drug treatment for relapsing remitting and early primary progressive MS. It is taken as an infusion into a vein or an injection under the skin every six months.

Octopus is a clinical trial evaluating several potential treatments for primary and secondary progressive multiple sclerosis (MS).

Opicinumab (also known as anti-LINGO-1 and BIIB033) was an experimental drug investigated as a treatment to promote myelin repair in multiple sclerosis. Clinical studies were halted in 2020.

Optic neuritis is a common eye problem where inflammation or demyelination affects the optic nerve. It is a condition in its own right, but is also strongly associated with multiple sclerosis. Not everyone who experiences optic neuritis goes on to develop further symptoms of MS, but a significant proportion do.

Orelabrutinib is a Bruton's tyrosine kinase inhibitor (BTKi) being tested as a new treatment for relapsing remitting multiple sclerosis (MS).

Although people with multiple sclerosis can't give blood or donate bone marrow, the donation of organs is allowed. Find out more about organ donations in this A-Z entry.

Osteoporosis is a condition that causes the bones to become thin and brittle, making them more prone to fractures. If you have multiple sclerosis, you have a higher risk of developing osteoporosis.

Oxybutynin is an anticholinergic drug that is used to improve your bladder's ability to store urine. In MS it may be used if you need to go to the toilet frequently, or if you have sudden urges to go to the toilet or find it difficult to 'hold on'. This is known as urinary frequency or urgency.

Learn about nerve (neuropathic) pain and musculoskeletal (nociceptive) pain in MS. Find out how common pain is, the causes and how it can be described.