Inclusion/Exclusion Criteria: All adults (≥18 year) with confirmed IBD on a biologic agent or with plans to initiate this within 1 month (defined as any anti-TNF, natalizumab, vedolizumab or ustekinumab) will be enrolled into a prospective cohort (initially in a pilot setting at 5 sites, later with full funding involving all sites of the CRA). Individuals with current biologic use will be included (i.e. prevalent users), with records collected as to time of initial biologic start, and prior specific formulations. Ideally, new initiators of biologic agents will be recruited at the visit where the decision is made to start a biologic agent. Those with a prior history of one of the 4 described paradoxical outcomes associated with a biologic agent will also be included as prevalent cases in order to increase the sample size, with appropriate clinical information collected per medical record. All data on prevalent cases will be entered historically prospective follow up with still occur to ensure that paradoxical reaction does not recur.