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Strong painkillers


Opioids are a type of painkiller - medicines used to treat severe or long-term (chronic) pain. Chronic means long-term and is the opposite of acute, meaning short-term, though some people sometimes wrongly use the word chronic to mean severe. Some opioids are stronger than others. The most common side-effects are constipation, feeling sick and tiredness. Other possible problems with opioids include dependence and addiction. When prescribed in the short term, for example in end-of-life care for cancer, addiction does not usually occur. In recent years we are becoming more aware that long-term opioid use is often not helpful, and guidelines are increasingly advising against it, as the risk of addiction is higher and the pain control may not be that good.

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What are opioids?

Opioids (sometimes called opiates) are medicines used to treat pain. There are many different types of painkillers that are suitable for different types of pain. Most doctors will start off prescribing a lesser strength painkiller such as paracetamol or ibuprofen. If these do not work, depending on the type of pain you have, your doctor may consider prescribing an opioid.

Types of opioids

Opioid medications are usually divided up into two groups:

Even though the strong opioids are classified together, they can also differ a lot in strength. The stronger ones may be ten times stronger than the weakest. Strong opioids are usually prescribed for more severe types of pain - for example, if you have had an operation or have been injured in a car accident. They may also be considered for people who have long-term pain, when other painkillers have not worked. They are also often used for pain in people with cancer.

The weaker opioids are usually taken as tablets. There are dispersible and liquid forms. They may come in brands which combine paracetamol and the opioid. Strong opioids can be taken as:

  • Liquid or syrup.

  • Quick-acting tablets and capsules.

  • Slow-release tablets and capsules.

  • Sachets.

  • Tablets that are held in the mouth - next to the gum (buccal tablets).

  • Patches for the skin.

  • Intranasally (fentanyl spray).

  • Injections, which may be under the skin, into the vein or into a muscle.

They all come in various different brand names and not all brands are the same. Once you have started taking one brand you should stick to the same one, unless your doctor has told you to switch to another.

Although there are quite a few strong opioids, the most commonly prescribed one is morphine. If your doctor thinks that a strong opioid would help your type of pain then morphine is often the first strong opioid to be prescribed. If this does not work, your doctor may consider switching you to a different one.

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How do opioids work?

Opioids work by attaching to opioid receptors in the brain and spinal cord, the gut and other parts of the body. This leads to a decrease in the amount of pain felt.

How are opioids taken?

Each different opioid medicine will have different instructions. Your doctor and pharmacist will explain exactly when and how to take them.


The principles of taking morphine are important and it is a good idea to understand how and why your morphine is prescribed in a certain way.

To start off with, you will usually be given a quick-acting strong opioid (morphine tablets or liquid) as well as a slow-release morphine tablet or capsule. The slow-release preparation is usually taken once or twice a day, depending on which brand you have been given. Slow-release preparations give a steady level of medicine in the body throughout the day. However, sometimes you can experience pain before you have your next dose of slow-release morphine; this is called 'breakthrough' pain. Quick-acting morphine is used to ease breakthrough pain. It can be taken every four hours, when you need to.

Your doctor will start you off on a low dose of slow-release morphine and increase this over a number of weeks until your symptoms have eased. It is really important to write down how much quick-acting morphine you are using each day. Your doctor can then use this information to increase the dose of your slow-release morphine in order to keep you pain-free.

Slow-acting morphine that is taken twice daily should ideally be taken 12 hours apart eg, at 8am and 8pm. If you take the two doses closer together, eg 10 hours apart, then the night-time gap between doses will be longer and your pain may recur.

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Side-effects of opioids

As with all medicines, opioids have a number of possible side-effects. In general, the stronger the opioid, the more likely you are to have side-effects. The most common side-effects are constipation, feeling sick (nausea) and drowsiness.

  • Constipation - when you start treatment with an opioid, your doctor will usually also prescribe a laxative. Laxatives help to ease and prevent constipation by softening the poo (stools), making it easier to pass, or they stimulate your bowel to push the stools along more quickly.

  • Nausea - feeling sick is a common side-effect when you first start taking an opioid. This usually passes after a week or so, once your body gets used to this medicine. Your doctor will prescribe an anti-sickness medicine (an antiemetic) if you feel sick. Tell your doctor if sickness lasts for more than a week. Changing to a different opioid may help.

  • Drowsiness and tiredness - again, this usually passes once your body becomes used to this medicine. Drinking alcohol as well as taking an opioid may increase drowsiness, especially at the start of treatment or when the dose is being increased. It is better to avoid alcohol if you are taking an opioid, or to drink less alcohol than usual.

A dry mouth can also be a problem. Some people find drinking plenty of liquids or chewing gum may help with this.

If the dose is too high, these medicines can:

  • Make you feel very drowsy.

  • Cause you to feel confused.

  • Make you feel dizzy or faint - signs of low blood pressure (hypotension).

  • Sometimes make you see things that are not there (called hallucinations).

  • Possibly cause you to have deep, slow breathing.

It is important to tell your doctor straightaway if you think you have any of these side-effects. The dose of your opioid may need to be decreased. If you have been wearing a prescribed fentanyl patch, remove it from the skin straightaway and speak with your doctor if you develop any:

  • Breathing problems.

  • Marked drowsiness and confusion.

  • Dizziness.

  • Slurred speech.

Addiction and dependence are also possible problems caused by opioids. These are discussed in the section below.

The above is not a comprehensive list - just the main possible side-effects to look out for. For a full list of possible side-effects, see the leaflet that comes with your medicine.

What is an opioid addiction?

Opioids, when taken for a long time, can cause tolerance, dependence and addiction. These are all different. Not everyone who takes opioids develops these problems. Dependence and tolerance occur more commonly than addiction.

Tolerance: if you have been taking opioids for a long time, they do not work as well as they did in the beginning. You may need a higher dose to treat your pain. This is called tolerance.

Dependence: if you gradually become more tolerant of the opioid, you may become dependent on it. This is NOT the same as addiction. It means that if you miss a dose, or stop the opioid suddenly, you may have withdrawal symptoms. You may need to keep taking the medicine to avoid the withdrawal symptoms. Dependence is treated by a planned gradual reduction in the opioid medicine. The dose is gradually reduced in such a way that your body can become used to it, so that you do not experience withdrawal symptoms. This does not mean you are addicted to the opioid.

Withdrawal symptoms: these occur if you have developed a physical dependence to opioids as above and then stop taking them suddenly. Withdrawal symptoms include:

  • Feeling anxious or agitated.

  • Not sleeping (insomnia).

  • Sweating.

  • Muscle pains.

  • Feeling sick or being sick.

  • Diarrhoea.

  • Tummy cramps.

  • Yawning.

Addiction: this is an excessive craving for the opioids. There is uncontrollable and compulsive use of the medicine. People who are addicted still have cravings for the opioids even after they have reduced them slowly so that they are no longer dependent. Some people are more likely to develop addiction than others and seem to be particularly sensitive to the cravings. It is unusual for people who are prescribed opioids for pain to become addicted to opioids.

What is the usual length of treatment?

This depends on the cause of the pain and the reason for treatment. Opioids may be taken for as long as they are helping to ease your pain. Some people take these medicines for many years. It is important to reduce the opioids if they are no longer needed. If opioids are being used for a long period of time, it is important that the doctor and patient have a clear discussion about the risks and benefits, and how to reduce the risks if possible.

You should also be told the following:

  • The type of medication and why it has been prescribed for you.

  • How the medication works.

  • The common side-effects and how long those side-effects may last.

  • The starting dose and when (and if) your doses will be adjusted.

  • How long the medication will take to work and how long you will stay on it for.

  • A contact person if you have any queries or concerns.

  • How long the medication in the prescription should last you - eg, seven days, two weeks.

  • The risks of addiction and overdose.

  • When you will have a review.

Sometimes, a patient may feel that an opioid drug would be useful and the doctor might disagree. In this case the doctor can refuse to prescribe the drug, if they feel that it would not be helpful or that the risks would outweigh the benefits.

How to stop taking opioids

You might want to think about stopping if any of the following apply:

  • There is no benefit or it is no longer helping you.

  • You have symptoms or signs of dependence.

  • The condition is resolved.

  • There are more harms than benefits to taking the medication.

  • You, as a patient, want to stop the medication

Do not suddenly stop taking opioids. This is because you may develop withdrawal symptoms (discussed above) if you stop them suddenly. If you want to stop taking these medicines, you should discuss this with your doctor and bring the dose down slowly. Many people find that after some time they can reduce their dose without their pain increasing. Your doctor will advise you.

Opioids and driving

You should not drive if are drowsy or confused because of our medication. You are more likely to feel drowsy at the start of treatment and when you have a dose increase. So it is sensible not to drive if you have just started taking an opioid, or if the dose has been increased. Once you are settled on the dose, if you do not have any side-effects which might affect your ability to drive, you may return to driving. It is your responsibility to judge whether you are fit to drive.

It's illegal to drive if you're unfit to do so because of prescribed opioid drugs. The police can stop you and make you do a 'field impairment assessment' if they think you're on drugs. This is a series of tests - eg, asking you to walk in a straight line. If they think you're unfit to drive because of taking drugs, you'll be arrested and will have to take a blood or urine test at a police station. Anyone with opiate and dependence should stop driving and inform the DVLA, who will remove their licence for at least six months.

Can I buy opioids?

Some weak opioids are available to buy over the counter at a pharmacy. This is mainly in the form of a low dose of codeine in combination with paracetamol. The dose is lower than the dose usually prescribed by doctors.

You cannot buy strong opioids. These medicines are only available on prescription, from a pharmacy. These medicines are also referred to as 'controlled drugs'. This means that they have to be stored in a special cupboard in the pharmacy and that doctors have to write these prescriptions in a certain way.

Travelling abroad

If you need to travel abroad with a strong opioid, you will need to check first with the embassy or high commission (of the country you are visiting) to see if they will allow you to take these medicines with you. If these medicines are allowed, you will then need a letter from your doctor which states the following:

  • Your name, address and date of birth.

  • The dates of travel in and out of the country and the country you're visiting.

  • A list of the medicines you're taking, the doses and the total amounts you're taking with you.

For people who are travelling for more than three months, a licence from the Home Office is required. Your doctor needs to fill in this form and send it to the Home Office. To obtain a licence you can:

Note: it can take up to two weeks for this form to be processed by the Home Office. It is best to allow plenty of time to apply for this licence.

Who cannot take opioids?

It is very rare for anyone not to be able to take some type of opioid. The main reason why you may not be able to take an opioid is if you have had a serious side-effect or an allergic reaction to a particular type of opioid in the past. Even if this happens, your doctor will usually be able to choose a different type of opioid, which you will be able to take.

In some groups of people, doctors only prescribe opioids very cautiously and at a lower dose. For example, this might apply if you:

Other considerations

There are a number of other considerations for opioids:

  • Storage - if possible, they should always be stored in a locked cupboard. They should be kept out of the reach of children.

  • After treatment stops - always return opioids to your pharmacy so they can be destroyed safely.

  • Take only as prescribed. Never take medicine which is prescribed for somebody else. Never take more than the prescribed dose. Only take opioids as advised by your doctor.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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