oesophagus – part of the gut between the throat and the stomach.
open label – this means that a patient in a trial knows which treatment they are taking.
opiate – a drug that comes from the opium poppy. Opiates include heroin, codeine and morphine.
opportunistic infection (OI) - an infection that occurs after your immune system has been damaged by HIV.
organogenesis – the process of development of baby’s main organs. This period is the first 12 weeks in the womb.
outreach – a type of service which goes out to find and engage people.