Opioids

Opioid analgesics comprise substances derived from opium (the opiates¹) as well as synthetic substances that act on opioid receptors in the body. Clinically, opioids are used mainly as analgesics but they can also be used for their cough-suppressant effect and to reduce intestinal motility. Some opioids are used in the management of opioid dependence².

Opioids form a key component in the World Health Organization’s ‘analgesic ladder’ for managing cancer pain.

Opioids are generally full agonists³ at the opioid receptor but some, such as buprenorphine and pentazocine, are mixed agonist–antagonist⁴ compounds. In addition to opioid agonist effect, tapentadol has noradrenergic activity which contributes to its analgesic effect. Tramadol is an opioid analgesic with noradrenergic and serotonergic⁵ properties which may also contribute to the analgesic effect.

The opioids diphenoxylate (combined with atropine as co-phenotrope) and loperamide are used for managing diarrhoea only; both are derived from pethidine. Loperamide is metabolised in the liver and very little of the intact drug enters the general circulation. Diphenoxylate has no analgesic effect; atropine is included in the formulation to deter abuse⁶ of diphenoxylate. Diphenoxylate and loperamide are not considered in the discussion of opioid risks, below.

In England, over 21.5 million primary-care prescriptions were dispensed for opioid analgesics in 2013; over 35% of these were for tramadol. A further 3.4 million prescriptions were for opioids licensed specifically for managing opioid dependency.