A Study to Investigate Efficacy and Safety of SAR441566 in Patients With Crohn's Disease.

To join this study, you generally need to be an adult between 18 and 75 years old and have been diagnosed with Crohn's disease for at least three months. Your Crohn's should be considered 'moderate to severe', which doctors measure using specific scores and tests like an endoscopy (a camera test to look inside your gut). You also need to have tried other common Crohn's treatments in the past, such as 5-ASA medicines, steroids, or stronger biologic therapies, but they either didn't work well enough, stopped working, or caused problems.

There are also some reasons why you might not be able to join. For example, if you have other specific gut conditions like ulcerative colitis or certain complications of Crohn's, such as active fistulas or recent bowel surgery. You also wouldn't be able to join if you have certain infections, including active tuberculosis, hepatitis B, or if stool tests show other infectious bugs. Women who are pregnant or breastfeeding cannot take part. The study team will review all your medical information carefully to see if this study is suitable for you.

If you decide to take part, the study will involve regular visits to a clinic over about a year – up to 59 weeks in total. This includes an initial check-up period of about four weeks. After that, for 12 weeks, you'll receive either the study medicine or the dummy pill. This is followed by a longer period of 40 weeks where you continue on the study treatment. Throughout this time, you will have various tests, such as blood tests, stool tests, and possibly endoscopies, to check how you are doing and track your symptoms. After the main treatment period, there will be a two-week follow-up to make sure you are well. Some participants might also have the option to continue receiving the study medicine openly for up to another 40 weeks, meaning you and your doctor would know you are getting the active drug.