For many people taking opioids, constipation is a fact of life. Among the drugs’ potential side-effects, opioid-induced constipation (OIC) ranks as perhaps the least welcome, with many patients choosing to forego the positive benefits of their medication in order to find relief from its distressing symptoms.

Dr Anton Emmanuel specialises in gastrointestinal issues at London’s University College Hospital.

‘Constipation is not a diagnosis but a set of symptoms encompassing an infrequent, difficult or incomplete opening of the bowel,’ he explains. ‘The symptoms of OIC are the same as in functional constipation, but arise as a result of taking medication.’  


‘Diet and exercise don’t help’


One of the major differences with OIC is that diet and exercise don’t play much of a role in helping to alleviate the symptoms. In fact, too much fibre and exercise – which would ordinarily help with digestive function – can make matters worse.

‘The usual instructions given to patients with constipation, such as drink more water, isn’t going to help with OIC,’ says Emmanuel.


Opioids affect the gut


When it comes to pain relief, opioids work by dampening down certain receptors in the brain responsible for pain perception. Those same receptors are also found in the stomach, colon and intestine, which means opioids affect them too and cause the same reduced response, resulting in constipation.

"One in five will reduce their opioids because the constipation is more distressing than the pain."

‘The gut is in constant dialogue with the brain, telling us if we’re hungry, full, or need to go to the toilet,’ says Emmanuel. ‘The same chemicals in the brain that make us feel happy also make us feel satisfied when we’ve eaten a meal. If we’re anxious or depressed, we can lose our appetite for much the same reason.’

In some patients with OIC, the symptoms are mild, but for others they can prove so distressing that they have a major impact on their quality of life. It’s not unusual for patients, including those with terminal cancer, to skip doses of their pain medication to bring about relief.

‘As many as one in five will reduce their opioids because the constipation is more distressing than the pain,’ says Emmanuel. ‘It can lead to anxiety and depression, which aggravates matters as patients can end up not eating very much, making their constipation worse.’



Laxatives offer limited help


For patients suffering from OIC, laxatives have traditionally been prescribed as the first line of defence, although it’s not one that always proves helpful and too many laxatives can lead to incontinence, resulting in further distress.

Where laxatives offer no help, there wasn’t a great deal that doctors could do but a new generation of drugs represents a big step forward in treating OIC.

Known by the acronym PAMORA, the drugs work by working on the pain receptors in the brain while leaving the same ones in the gut untouched.

‘For doctors initiating opioid treatment, it’s best to think about the bowel from the outset. Most patients will be affected, so talk to patients from the beginning and make laxatives available. Don’t wait until they come back with issues,’ Emmanuel advises.