The Oxford English Dictionary (OED) defines an opioid as "any synthetic narcotic drug derived from or having properties similar to those of morphine" and an opiate as "any drug derived from opium, esp. morphine and codeine".
It is important to distinguish between 'opioids' and 'opiates', as this affects data collection and categorisation that ultimately impacts policy. For example, the UK's Office for National Statistics (ONS) collects data on deaths related to drug poisonings. In their annual report, they display deaths involving "any opiate", "heroin or morphine", and "methadone", rather than all opioids, owing to variation in reported data. There is also a smaller number of opiates compared with opioids.
The OED defines a narcotic as "a drug which when swallowed, inhaled, or injected into the system induces drowsiness, stupor, or insensibility, according to its strength and the amount taken; esp. an opiate." The term narcotic is a legal term for drugs that are abused and so also includes non-opioid substances, such as cannabis and cocaine. For example, the International Narcotic Control Board (INCB) regulates 136 narcotic drugs and collects global narcotic consumption statistics and includes data on raw materials for the manufacturing of narcotics.
For the Catalogue of Opioids, we defined an opioid as medicaments that targeted or had an effect or coeffect at one or more opioid receptors, including mu (MOP), delta (DOP), or kappa (KOP) receptors, or the nociceptin receptor (NOP) (Richards et al. 2021). We excluded medicaments that did not have an IUPAC name (e.g. opium), raw opioid-related materials, endogenous opioids or opioids that were metabolites, peptides, intermediates or analogues unless they were synthesized as medicaments. Using this definition, we also include opioid antagonists (e.g. naloxone) and opioids used as antidiarrheals (e.g. loperamide) and cough suppressants (e.g. dextromethorphan), which is important as most previous research has focused on opioid analgesics alone.