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Opioids are a group of medicines that come from the extract of poppy seeds or other medicines that work in the same way.

Types of opioid

The first opioids came directly from the poppy seed and include medicines such as morphine and codeine. Other commonly prescribed opioids are similar to morphine but have been changed chemically and include oxycodone and buprenorphine. A final group of opioids are completely unrelated chemically to morphine but work in a similar way. Examples include tramadol, and fentanyl.

Some opioids, particularly codeine and dihydrocodeine, may be helpful for moderate pain. You can get certain strengths of them at pharmacies, combined with paracetamol (co-codamol and co-dydramol). Most other opioids are only available on prescription and used for severe pain.

How do opioids work?

Opioids act directly on several parts of the pathway that process pain in the nervous system (spinal cord and brain) to block the way pain signals are transmitted. Opioids are some of the strongest pain-relieving medicines available and are used to treat pain after surgery, serious injury and cancer. Opioid drugs may help some, but not all, types of long-term pain such as arthritis, back pain and neck pain.

Before taking an opioid for long-term pain

You should discuss with your doctor or other healthcare professional what you expect from treatment with an opioid medicine.

Pain-relieving medicines (painkillers) are generally the first step in treating pain after surgery or an injury. However, it is rarely possible to relieve long-term pain completely with painkillers. The aim of treatment is to reduce your pain enough to help you get on with your life. In trials, most medicines for long-term pain (including opioids) on average only reduce pain by 30%, and only help around one in every four or five people.

Medicines work best if you combine them with other ways of managing symptoms, such as regular activity and exercise, and doing things that you enjoy, such as work or study and social activities. Setting goals to help improve your life is an important way to see if these drugs are helping.

‘Why don’t my pain relieving medicines work?’ is a common question, and often one without any easy answers. Long-term pain can be due to many factors, and most drugs only work for one of these factors. Some pains do not seem to respond to any pain relieving medicines. You can get used to pain relieving medicines, including opioids, so that you need more and more to have the same effect. (This is called tolerance.) However, high doses of opioid medicines taken for long periods are unlikely to give better pain relief and can have problematic side effects.

How do I take opioids?

Opioid medicines come in many different forms, such as injections, tablets, capsules, liquids, and patches. The way each medicine is taken varies and your healthcare professional may be able to answer any questions you may have.

Before you start taking an opioid, read the manufacturer’s printed information leaflet from inside the pack. This will give you more information about the specific medicine you have been prescribed, and a full list of the side effects which you may experience from taking it.

When should I take my opioid medicine?

For continuous long-term pain, you may be given a slow-release tablet or an opioid skin patch which delivers a steady amount of medicine in the blood. Your healthcare professional may adjust the dose to try and give you relief from the pain most of the time and so that you don’t get too many side effects. Fast-acting opioid medicines and opioids that are injected are not very useful for managing continuous pain.

What dose of opioid should I take?

The correct dose for any medicine is the lowest dose that produces a noticeable benefit to allow you to get on with life. It is not usual to get complete relief of pain from opioids.

You should always take the correct dose of prescribed opioid medicines. If you feel the dose isn’t enough, or if side effects interfere with your life, you should discuss this with your healthcare professional.

How long will an opioid medicine take to work?

This depends on the form of opioid you have been prescribed. You may be given fast-acting tablets when you first start trying opioids, and these may work within an hour and last for around three to four hours. For long-term pain, tablets or skin patches are more common. Slow-release tablets or patches take longer (up to two or three days) to begin to have any noticeable effect.

What are possible side effects of opioid medicines?

When you first start taking opioid medicines you may get some side effects, which usually stop after a few days. These include:

  • feeling dizzy
  • feeling sick (nausea)
  • being sick (vomiting)
  • feeling sleepy
  • feeling confused.


Sometimes these side effects can go on for longer than a few days. Your healthcare professional may give you some other medicines to help, such as anti-sickness tablets.

Opioid medicines can cause some problems when you take them for long periods. These include the following.

  • Constipation


Constipation is a common problem when taking opioids and does not tend to go away the longer you take opioid medicines. You can help yourself by drinking plenty of liquids, and eating fresh fruit, vegetables, bran and prunes. You may need to take laxatives such as senna and docusate. If you experience a lot of side effects your healthcare professional may suggest changing to a different opioid medicine.

Other side effects include:

  • itching
  • weight gain
  • lack of sex drive
  • difficulty breathing at night.


You are more likely to have difficulty breathing at night if you are overweight and if you snore heavily. If you have a condition called obstructive sleep apnoea it may not be safe for you to take opioids. It is best to discuss this with your healthcare professional.

What if I forget to take a dose or miss a dose?

Take it as soon as you remember. However, if it is almost time for your next dose, skip the missed dose and take the next dose as normal. Do not take two doses together.

Can I drink alcohol?

Both alcohol and opioids can cause sleepiness and poor concentration. It is best to avoid alcohol completely when you first start on opioids or when your dose has just been increased. If you are taking opioids, you should avoid alcohol if you are going to drive or use tools or machines. Once you are on a steady dose of opioid, you should be able to drink modest amounts of alcohol without getting any extra unusual effects.

Will my body get used to opioid medicines?

Opioid medicines sometimes become less effective with time (this is called tolerance). This means that your body has got used to the pain-relieving effect of the medicine.

You can also become dependent on opioid medicines. This means that if you stop taking the drug suddenly, or lower the dose too quickly, you can get withdrawal symptoms. If you run out of medicine, you may experience the same symptoms. These include:

  • tiredness
  • sweating
  • a runny nose
  • stomach cramps
  • diarrhoea
  • aching muscles.

What about addiction to opioid medicines?

We do not know exactly how many people get addicted when they are taking opioids for pain relief but it is uncommon.

People who are addicted to opioids can:

  • feel out of control about how much medicine they take or how often they take it
  • crave the drug
  • continue to take the drug even when it has a negative effect on their physical or mental health.


Addiction is more common if you have been addicted to opioids (including heroin) or to other drugs (or alcohol) before. Addiction may be more common in people with severe depression or anxiety. This does not mean that if you have had an addiction problem before or you are very depressed and anxious you will become addicted. It only means that you are more likely to become addicted than someone who has not had these problems.

So, if you have had a problem with drug or alcohol addiction in the past this doesn’t mean that you cannot take opioid medicines for your pain. However, your healthcare professional will need to know about your past or current drug-taking to prescribe opioids safely and to help you watch out for warning signs.

Is there anything else the person prescribing my opioid medicine needs to know?

They will need to know if:

  • you are allergic to any drugs or medicines
  • you are taking any other medicines or herbal medicines
  • you are pregnant or breast feeding, or if you are planning to become pregnant
  • you are asthmatic or have other breathing problems
  • you have any heart, kidney or liver disease
  • you have a history of epilepsy or fits
  • you have hypothyroidism (an underactive thyroid)
  • you have an enlarged prostate or problems urinating
  • you have chronic (long-term) constipation or a bowel obstruction
  • you have a kidney or liver problem
  • you have or have had a history of excessive alcohol use, recreational drug use or addiction to prescribed or over-the-counter medication.


Can I drive when I am taking an opioid medicine?

You must not drive if you feel sleepy, dizzy, are unable to concentrate or make decisions, have slowed thinking or reactions, or if you experience sight problems. You should not drive for at least five days when you first start taking a strong opioid pain relieving medicine, or if you are changing the dose. This gives time to ensure that you are not experiencing side effects which might affect your ability to drive safely. Remember that alcohol taken in combination with medicines, even in small amounts can greatly increase the risk of accidents.

You should tell your car insurance company about your current state of health, and what medicines you are taking. Each insurance company is different, but your insurance may not be valid if you do not do this.

New drug-drive legislation came into force on 2 March 2015 in England and Wales which places limits on the amounts of certain drugs that you can have in your blood stream while driving. As long as you are following the advice of a healthcare professional and your driving is not affected, you can continue to drive as usual and are not at risk of arrest. Keep some suitable evidence with you when driving to show that you are taking your medicine as prescribed or supplied by a healthcare professional.

What if I want to stop taking an opioid medicine?

When making the decision to take strong opioids, it is important to set yourself goals which can help you measure the benefits of the medicine. If the medicine allows you to be more active or return to work, for example, you may well decide that it has done a good job. If the medicine does not help you to live a fuller life, it may be appropriate to talk with your healthcare professional about reducing and stopping them.

You may experience withdrawal symptoms if you stop using opioids suddenly. Speak to your healthcare professional who will be able to supervise a gradual reduction.


Dr Roger Knaggs is Associate Professor at the School of Pharmacy, University of Nottingham and Fellow of the Faculty of Pain Medicine.


The regulations controlling medicines change from time to time. For the latest information, please visit


This information is not intended to replace your doctor’s advice. We advise you to read the manufacturers information for patients, which your pharmacist will give you with your medication. Keep all medicines away from children.



Other leaflets in this series include Antidepressants and Gabapentin and pregabalin. You might also like our Managing your medications leaflet.

Opioids © Roger Knaggs. All rights reserved. October 2017. To be reviewed October 2020.


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