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Opioid Drugs

What are Opiates and Opioids?

One of the earliest groups of drugs used for pain, dating back many millennia, are the opiates.  These still have a valuable role in the management of pain nowadays. Some of these drugs are derived form the opium polly, papaver somniferum, and these drugs are called opiates.  Research has allowed the development of a number of other drugs which work in the same way as these drugs, not all of which are directly derived from opium. These, as a group, are called opioids.

Opioids affect receptors in our nervous systems and elsewhere in our bodies and by acting on these receptors have a number of effects and side effects.  

Some very useful information for patients about opioids is given in a booklet published by the British Pain Society titled Opioids for persistent pain: information for patients (2010).  This leaflet has been produced in conjunction with the publication for health professionals, 'Opioids for persistent pain: Good practice', which is linked from the page on information for professionals.

A copy of this document can be downloaded free of charge from the British Pain Society's website here.



There is also a newly-published website on the Faculty of Pain Medicine site, called "Opioids Aware", which has excellent information and which we highly recommend.

Different Opioids

Opioids work by binding to receptors in the body. When they bind they are mimicking the effects of the body's natural opioids, which are called endorphins and enkephalins. Once bound to the receptors, the opioids stimulate mechanisms to reduce the firing of the neurones, leading to a decrease in pain.  These actions take place in various parts of the brain and nervous system:

  • Areas in the brain which are involved with the detection of pain.
  • Areas in the brain which are involved in the emotional response to pain (you may not react in quite the same way to your pain as you have done previously).
  • Receptors in the spinal cord which are involved in the transmission of pain (reducing the pain signals travelling to the brain).
  • In inflammation, they may have an effect in the painful tissues themselves.

 The way that opioids and other drugs bind to their receptors can affect their effectiveness.  Some opioids have strong actions, and these are termed full agonists; some have weaker actions and are termed partial agonists.  Some drugs can prevent opioids from acting at their receptors, and are called antagonists.

This means that there are many opioids with varying strengths (and side effects).  Some details of these can be found at this table.


Side Effects of Opioids

The receptors on which opioids work are present in a large number of areas in both the nervous system and the rest of the body.  Unfortunately, this can result in these drugs having actions in other areas than the pathways involved in pain sensation.

The side effects which opioids commonly produce include:- 

  • Constipation. This is very common and is often a persistent problem.
  • Nausea. This may occur at the start of therapy. It usually passes after a short time.
  • Sleepiness, fatigue, dizziness and mental clouding. These are common at the start of therapy and usually pass after a short while.
  • Itch
  • Urinary retention
  • Dry mouth
  • Sexual dysfunction

Rarer side effects include reduction in bone density and changes in sex and other hormones, and potentially effects on the immune system.


Opioid drugs can cause breathing to slow and, in overdose, can be lethal. Breathing problems of this type are very rare when these drugs are administered in an appropriate way. 

 Among the most feared effects of the opioid drugs are those related to the problem of chemical dependency. There is a great deal of misconception about this issue. Opioids, like a number of other drug classes, have the potential to be abused or diverted into the illicit marketplace. Addiction is a concern. There is often confusion about the meaning of the word "addiction" and how much risk there is. To assess this, the first step is to define the problems correctly. 

Addiction is a disease that has a genetic aspect (a biological part) and a psychosocial aspect and is diagnosed by the development of drug-related behaviors consistent with 1) compulsive use of a drug, 2) loss of control over the drug, 3) craving for the drug, and 4) continued use of the drug despite harm to the user or others. 

Physical dependence means that a person will probably have withdrawal if the drug is stopped or an antagonist drug is given. This physiological process, which occurs with many other types of drugs, is not the same as addiction and should never be called addiction. In practice, withdrawal typically does not occur if the drug is not stopped suddenly, and for this reason, physical dependence is not a major concern. 

Tolerance is another physiological process defined by the gradual loss of effect over time as the body gets used to the drug. Tolerance to nausea and mental clouding occur commonly. Tolerance to pain relief is not a major problem in the clinical setting. 

Abuse is a term that means that the drug is not being used in a responsible way. Either a drug is being used outside of social norms, or in a way that is contrary to how it was prescribed. 

Aberrant drug-related behavior is the term applied to the use of drugs in a manner that suggests some type of problem. It could be abuse or addiction, or it could be a lack of understanding or desperation that comes from uncontrolled pain. Clinicians should always monitor patients for the development of these problems, determine the cause, and then act accordingly. 


Opioids and driving

The MHRA have just (2014) released an information leaflet on driving while on certain medications, including opioids, which is linked here. Further information on this is linked here.



Opioids Aware

 The Faculty of Pain Medicine of the Royal College of Anaesthetists has produced a very useful information site on opioid prescribing, Opioids Aware.  This has content which is very useful both for lay people and professionals.


Other resources

The British Pain Society has produced an information booklet "Opioids for Persistent Pain: Information for Patients" which can be downloaded here.

While the use of opioids for chronic non-cancer pain is commoner nowadays than it was, it is not without resulting issues and problems.  In this video presentation from the Pain Community Centre in Cardiff, our colleague Dr Cathy Stannard discusses these.

 Further details is given in the Gloucestershire Joint Formulary website, and on this is a useful opioid equivalence chart.  This chart may also be helpful.  A useful resource for considering the various costs of opioid preparations can be found here.

 The Scottish Intercollegiate Guidelines Network (SIGN) has published, in November 2013, guidelines on Chronic Pain including a comprehensive advisory pathway on prescribing of opioids, which should hopefully also be helpful.


Recommended viewing

Currently still available on IPlayer, apparently until November 2016, is an excellent Panorama programme called "Hooked on Painkillers" which dealt very will with the issues of using opioids for Chronic Pain.  We would very highly recommend this.  It is also mentioned on the Pain Concern website.



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Pain Service Website, Gloucestershire Hospitals NHS Foundation Trust
Webmaster Dr J G de Courcy, Consultant in Pain Medicine and Anaesthesia
email: pain.webmaster[at]

Page updated 4/7/2016