Clinical trial results described as "striking and exciting" could lead to new treatment options for rheumatoid arthritis.
The antibody drug tocilizumab was almost four times more likely to halt progression of the condition than the most widely prescribed alternative.
It also achieved significantly greater reduction in disease signs and symptoms after six months.
Scientists compared tocilizumab, marketed as RoActemra, with the "anti-TNF" drug adalimumab (Humira).
The drugs were tested in a group of 326 patients unable to take the mainstay treatment for rheumatoid arthritis (RA), methotrexate (MTX)
MTX is ruled out for roughly a third of patients, many of whom suffer unbearable side effects such as vomiting, hair loss and mouth ulcers.
Currently, such individuals generally move onto anti-TNF drugs, which target a molecule called tumour necrosis factor that promotes inflammation.
Tocilizumab works in a completely different way by targeting another inflammatory protein, interleukin six (IL-6).
Consultant rheumatologist Professor Paul Emery, from the University of Leeds, who took part in the Adacta trial, said: "These results are impressive and important for the 30 per cent of patients with RA who cannot take methotrexate.
"In RA, disease remission is the goal of therapy.
"However, for varied reasons, many patients fail to achieve this goal.
"Adacta, which compared two active biologics as monotherapies (in methotrexate intolerant patients), has produced striking results and the results help in choosing the right drug for the right patient."
The findings were presented in Berlin at Eular, the annual meeting of the European Congress of Rheumatology.
RA is a painful and disabling condition caused by the immune system attacking the joints.
Of those newly diagnosed, around a half will be unable to work within 10 years.