Background: The epidemiology of inflammatory bowel disease (IBD) in the UK is poorly described. Primary care contraceptive prescribing data published by the NHS are not linked to individual patients. Studies have linked contraceptive pills to the development of IBD. However, there is a paucity of literature on how contraceptive formulation and duration of therapy affect IBD risk.

Aims: To describe changes in the incidence and prevalence of IBD in the UK from 2000-2018. To describe non-barrier contraceptive prescribing patterns in primary care over the same period. To investigate the associations between exposure to contraception and development of IBD.

Methods: Three epidemiological studies using IQVIATM Medical Research Data; a cohort study examining temporal trends in IBD incidence and prevalence, a repeated cross-sectional study exploring trends in contraceptive prescribing, a nested case-control study investigating the associations between a range of contraceptives and development of IBD.

Results: Overall, the incidence of IBD is falling, but prevalence continues to rise. Some of the highest recorded incidence and prevalence rates globally were observed, with a 94% rise in incidence in adolescents since the year 2000. Over the same period, combined hormonal contraception prescribing has halved whereas progestogen-only pill prescribing has more than doubled. Methods of contraception prescribed by GPs are influenced by social deprivation. Withdrawal of a pay-for-performance incentive may have adversely affected adolescent long-acting reversible contraception uptake. Results suggest that oestrogen-containing contraception is associated with development of IBD whereas progestogen-only methods have minimal to no effect.

Conclusion: This thesis provides evidence relating to a wide range of temporal trends in the epidemiology of IBD and patterns of contraceptive prescribing in the UK. Although previous associations between oral contraceptive pills and IBD have been made, this thesis provides the first epidemiological evidence that oestrogen-containing contraceptives, but not progestogen-only methods, are associated with development of IBD.