Dr Willcox has worked as a GP in the NHS since 2003 and currently works in a practice in Oxford as well as in the Out of Hours service. His research interests include global health, clinical trials of herbal medicines, and improving care for vulnerable people. His research interests at the University of Southampton focus on the care of vulnerable people, global health, and traditional (particularly herbal) medicine.

Dr Willcox has researched different aspects of primary health care in low-income countries, with a particular focus on child health, malaria and traditional medicines. He led a pilot confidential enquiry into maternal and child deaths in Uganda and Mali from 2011 to 2015. He has been involved in several clinical trials of herbal medicines in Uganda, Madagascar, Mali and the UK and coordinates the RITAM network (Research Initiative on Traditional Antimalarial Methods).