A 'patient safety incident' is an unintended or unexpected incident that led to, or could have led to, patient harm. A patient safety incident involving medicines is known as a 'medication safety incident'. NHS England defies a 'serious' incident as one that results in any of the following:

• Unexpected or avoidable death of patients, staff, visitors or members of the public
• Serious harm to one or more patients where the outcome requires life-saving intervention, major surgical/medical intervention, or the outcome causes permanent harm, will shorten life expectancy or result in prolonged pain or psychological harm
• Allegations of abuse
• One of the never events. Never events are a sub-set of 'serious incidents' and are defined as 'serious, largely preventable patient safety incidents that should not occur if the available preventative measures have been implemented by healthcare providers'.

Medication-related examples include:

• Death or severe harm as a result of an opioid overdose given to an opioid naïve patient
• Prescription, supply or administration of daily oral methotrexate to a patient for non-cancer treatment, including supply to the patient with the instruction to take daily
• Death or severe harm as a result of oral/enteral medication, feed or flush administered by any parenteral route.