Although weight gain or weight loss are not listed as side effects in the manufacturer's product information for Cosentyx, anecdotally several people have reported weight gain, some of which was significant, during Cosentyx treatment. But most people who gained weight decided to continue with Cosentyx treatment because it had effectively cleared their psoriasis or psoriatic arthritis. Weight loss has been noted as a rare side effect of Cosentyx in post-marketing reports.

For people who gained weight, most report gaining up to 20 lbs (9kg) around their stomach area and lower back, despite their diet remaining the same or less than it was before they started taking Cosentyx and exercising more. It is important to understand that with anecdotal reports, it is impossible to know if the weight gain was due to the medication or some other factor.

There is also some evidence that other interleukin inhibitors, such as tocilizumab (Actemra) can cause weight gain and early research has suggested that the IL-6 pathway is involved in weight regulation. Other interleukin pathways may also be involved in weight regulation.

If you do gain weight while taking Cosentyx, talk to your doctor about it, and ask them to consider testing you for diabetes or insulin resistance, which weight gain is a symptom of. FDA data that analyzed data from 116,009 people with side effects from Cosentyx found 749 of them (0.65%) had Diabetes. Diabetes is more likely among people who take Cosentyx who are female, aged 60 and older, and who have been taking Cosentyx for 1 - 6 months.

Cosentyx is a biologic therapy that contains secukinumab, a human monoclonal antibody. It works by selectively binding to interleukin 17A (Il-17A), reducing inflammation which is characteristic of conditions such as plaque psoriasis, psoriatic arthritis, and ankylosing spondylitis.