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The molecular structure of Fentanyl
  • Fentanyl is a synthetic opioid which acts as an analgesic. The drug is similar to morphine; however, it is 50 to 100 times more potent.

    Fentanyl is typically used to treat severe pain and is available on prescription. The drug is also synthesised illicitly and sold for illicit use.

    Many analogues of fentanyl have been developed. Some for use in medicine (e.g., alfentanil) and veterinary medicine (e.g., carfentanil) along with illicit analogues (e.g., alpha-methyfentanyl). These are commonly referred to as fentanyls and have caused sudden deaths, often when heroin has been laced with one of them. Their potency varies and can be much higher than that of fentanyl.

  • Fentanyl itself exists as a white powder that dissolves in water. It is often administered to patients in the form of a lozenge, transdermal patch or by injection.

    Illicitly produced fentanyls may also appear as a grey or off-white powder. Eye droppers, nasal sprays and tablets designed to mimic prescription pills containing fentanyls have been observed on the drug market.

  • Medicinal fentanyls can be administered by intravenous injection, transdermal patches, tablets and lozenges.

    Outside of medical use, fentanyls are used in many ways. They can be snorted, injected intravenously, smoked and ingested via oral sprays. People may also chew on prescription fentanyl patches to release the contents into their mouth.

    Illicit fentanyls are also often mixed with other drugs such as heroincocainemethamphetamine and MDMA. Fentanyls have high potency, making them a cheaper option to produce and transport. This, therefore, can lead to users accidentally ingesting fentanyls when intending to consume a different drug.

  • Like other opioids, fentanyls bind to opioid receptors in the brain (predominantly the µ-opioid receptors), in areas which control pain and emotion in humans.

    Tolerance and dependence rapidly develop after repeated use of fentanyls.

  • Depending on the mode of administration, the effects of fentanyls can be felt immediately (injection), or in around 15-30 minutes (tablets, lozenges and nasal sprays). When injected, the effects last for around 30-60 minutes. Whereas, when ingested via tablets, lozenges and nasal sprays, the effects last for up to 4-6 hours.

    These effects include

    • Euphoria

    • Drowsiness

    • Sedation

    • Nausea

    • Confusion

    • Constipation

    • Muscle stiffness

    • Respiratory depression

  • Fentanyl itself was first synthesised in 1960 and used to treat severe pain. It is still used in medicine for this reason.

    It may be administered along with a general anaesthetic agent during surgery and is often prescribed to people after operations or after serious injuries. It can also be used to treat pain experienced by cancer patients. People experiencing chronic pain may also be prescribed fentanyl if other pain medicine they have been using is no longer effective.

  • Overdose

    Taking an overdose of fentanyl leads to respiratory depression, which can cause brain damage and death. The lethal dose of fentanyl is approximately 2 mg in humans.

    Fentanyls rapidly penetrate the brain and so respiratory depression and death can occur very rapidly. In addition to reducing the rate of breathing, fentanyls also produce muscle stiffness in the diaphragm and chest muscles (referred to as wooden chest) making it harder to breathe.

    The effects of overdose can be temporarily reversed by administering naloxone. It may be necessary to administer more/higher doses of naloxone to reverse fentanyls than for heroin. Medical assistance should be sought immediately when an overdose is suspected.

    If a person has taken an overdose, they may fall unconscious and become limp. Their skin may also become clammy, and the fingertips and lips of lighter-skinned people and the inside of darker-skinned people’s lips may turn blue.

    To reduce the risk of overdose, users should start by taking a small dose and see how they feel, rather than taking a large dose all at once. It is also advised to have a trusted person around when using fentanyls, so that they can aid in the event of overdose.



    Fentanyls are addictive drugs due to their high potency and the rapid rate at which tolerance to them develops.

    Addiction can occur both following illicit use and with repeat prescriptions. Those who take fentanyl as prescribed by a doctor may become dependent and experience withdrawal symptoms when their prescription ends.

    Withdrawal symptoms include:

    • Muscle and bone pain

    • Difficulty sleeping

    • Diarrhoea and vomiting

    • Cold flashes

    • Uncontrollable leg movements

    • Severe cravings

    If you are using fentanyls, it is important to be aware of the signs of addiction and tolerance. For example, experiencing strong cravings and requiring increasingly higher doses to produce the same effects. Medical help is available to those experiencing addiction.

  • There are a few health conditions which may make using fentanyls more dangerous. For example, any lung conditions (such as asthma) and arrhythmia (irregular heartbeats).

    Some people are allergic to fentanyls and may go into anaphylactic shock after use.

  • Fentanyls should never be mixed with other drugs.

    It is especially dangerous to mix fentanyls with other opioids, alcohol, or other sedative drugs such as benzodiazepines or gabapentinoids. Mixing fentanyls with these drugs greatly increases the risk of overdose.

    When fentanyls are used as an adulterant for other drugs, the risk of overdose is increased as the user is most likely unaware of the amount of the fentanyl present. Drug testing kits are available to detect the presence of fentanyls and should be used to reduce the risk of accidental overdose when consuming an illicit drug which may be adulterated with them.

  • Fentanyls can be very addictive.

    Fentanyls can produce a very pleasurable experience for users, leading them to want to use the drug continually. When using fentanyls repeatedly, tolerance to the drug increases and withdrawal symptoms are experienced between doses. Users may then take the drug in order to cope with these unpleasant withdrawal effects, and an ever-increasing dose is required to produce the same effects. Use of the drug often becomes less pleasurable over time and is more used to soothe withdrawal symptoms than for any euphoric experience.

  • Withdrawal symptoms include:

    • Muscle and bone pain

    • Difficulty sleeping

    • Diarrhoea and vomiting

    • Cold flashes

    • Uncontrollable leg movements

    • Severe cravings

    As with any drug addiction, addiction to fentanyls can cause problems at work or school and put strain on relationships with family and friends, as well as the physical and mental health issues that can ensue. People who are addicted to fentanyls will continue to use them despite these issues and may engage in risky behaviour in order to obtain more of the drug.

  • Long-term use of fentanyls can lead to organ damage, respiratory issues (if smoked) and brain changes, alongside the emotional damage that addiction to fentanyl causes.

    Injecting fentanyl carries an increased risk of infection from viruses (such as hepatitis B or C) or bacteria, especially when sharing needles with other people. Injecting repeatedly causes scarring of veins and leads to their collapse.

  • Avoiding use, minimising use, avoiding addiction.

    Whilst the body does not immediately develop a physical dependency, people will often like the drug and want to repeat the experience from the first use. If you encounter fentanyls regularly in your social or family life, this constant availability will add to the temptation to repeat an initial experience, as will stresses in life.

    If you do use fentanyls occasionally and do not wish to stop despite the risks, it is important to be vigilant and reactive to signs of dependence. Growing tolerance for fentanyl (needing more to feel the same effects) is an important warning sign of some of the changes in your brain chemistry that lead to cravings and withdrawal effects when you don’t use.


    How are you taking it?

    Injecting fentanyls carries with it more risks than smoking or snorting them. Firstly, with fentanyl injection the total dose is taken in one go, so it is easier to overdose. It is much better to take a small amount to start with. As injecting fentanyls produces such a big rush, it is easier to become addicted to fentanyls when injecting.

    If a user is injecting, they can still do many things to reduce unnecessary harms. Deliberately, or accidentally sharing used needles and syringes carries the risk of infection from viruses such as HIV and Hepatitis B or C. Using new sterile equipment reduces the risk of infection. In many countries, advice on safer injection and free equipment can be accessed at needle exchanges.


    Are you taking anything else? Mixing other drugs with fentanyls can be very risky

    Taking fentanyl with any other drug that can stop breathing (e.g., alcohol benzodiazepines or gabapentinoids) increases the risk of overdose. Additionally, taking fentanyls with stimulants like cocaine and speed (amphetamine) can increase the risk of overdose. This is due to the tendency to take a redose of both the stimulant and the fentanyl when the stimulant wears off. The effects of the stimulant often wear off more quickly than the fentanyl, leading the user to take an overdose of fentanyl.

    When using fentanyls, it is a good idea to carry naloxone in case of overdose. Users will not be aware when they are overdosing, so trusted people should be present when using fentanyls. This means that they can administer naloxone if an overdose is suspected. Whilst medical assistance should be sought immediately when overdose is suspected, naloxone can neutralise the effects of overdose whilst waiting for medical help to arrive. Naloxone binds to the same receptors as fentanyls do, preventing the fentanyl from binding and producing any further effects.

  • Is fentanyl resistant to naloxone?

    No, fentanyl and its analogues are not resistance to naloxone. Due to its potency, more may be required to treat an overdose, however, naloxone still targets the same receptors that fentanyl does.


    Can you overdose by touching fentanyls?

    No, it is not possible to overdose simply by touching fentanyls. The drug must enter the bloodstream or come into contact with a mucus membrane in order for the effects to be experienced. Transdermal fentanyl patches have a specific formulation which allow the drug to be absorbed via the skin.

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