Merck Manual

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Opioid Analgesics

Opioid Analgesics

Drug

Length of Effectiveness

Comments

Morphine

By injection into a vein (intravenous) or muscle (intramuscular): About 3 to 4 hours

Immediate-release form by mouth: About 4 hours

Controlled- and sustained-release forms by mouth: 8 to 24 hours

Morphine starts to work quickly. The oral form can be very effective for chronic pain. It is more likely to cause itching than other opioids.

Buprenorphine

By injection into a vein, under the skin, or muscle: About 6 hours

By skin patch: Up to 1 week

Between the gums and cheek: 12 hours

Buprenorphine has some of the effects of opioids but also blocks some of the effects of opioids. It is occasionally used to relieve chronic pain and may be substituted for a stronger opioid to help people who are addicted to opioids stop taking them. It may be the preferred opioid for older people because it has fewer side effects (such as constipation and respiratory depression) and can be used more safely in those with a kidney disorder. However, buprenorphine can cause withdrawal symptoms when given to people who have opioids in their system.

The skin (transdermal) patch is re-applied once a week.

For pain, the forms most commonly used are a skin (transdermal) patch or a film placed under the tongue.

Codeine

By mouth: About 4 hours

Codeine is less potent than morphine. It is usually taken with aspirin or acetaminophen.

Fentanyl

As lozenges or dissolvable tablets: 2 to 4 hours

By spray into the nose or under the tongue: 2 to 4 hours

By skin patch: up to 72 hours

Fentanyl lozenges and dissolvable tablets can be used to treat breakthrough pain (a brief, often severe flare-up of pain that may occur during treatment for chronic pain).

Fentanyl lozenges can also be used to relieve pain and provide sedation (before painful procedures) in children.

A fentanyl patch is often used to treat chronic pain.

Hydrocodone

By mouth: 4 to 6 hours

Hydrocodone is similar to codeine in effectiveness.

Hydromorphone

By intravenous or intramuscular injection: 4 to 6 hours

By mouth: 4 to 6 hours

By rectal suppository: 6 to 8 hours

Extended-release form: 24 hours

Hydromorphone begins to work quickly. It can be used instead of morphine and is useful for chronic pain.

The rectal suppository is used at bedtime.

Levorphanol

By intravenous or intramuscular injection: 6 to 8 hours

By mouth: About 6 to 8 hours

The oral form is strong. It can be used instead of morphine.

Meperidine

By intravenous or intramuscular injection: About 4 hours

By mouth: Not very effective

Meperidine can be effective for short-term use. But long-term use is discouraged because meperidine has side effects, such as muscle spasms, tremors, seizures, and confusion or delirium (especially in older people). Some health care practitioners prefer not to use it.

Methadone

By mouth: 6 to 8 hours, sometimes much longer

By intravenous or intramuscular injection or injection under the skin (subcutaneous): 6 to 8 hours

Methadone is used for treating addiction to heroin and other opioids. It can also be used to treat chronic pain.

Methadone can have serious side effects, especially when it is first started. For example, it can cause breathing to become dangerously slow or to stop within days after people start taking it, even without an increase in the dose taken. To prevent serious side effects, people must be careful to take the drug as directed.

Oxycodone

Short-acting form by mouth: About 4 to 6 hours

Long-acting, controlled-release form by mouth: About 12 hours

Oxycodone can be used instead of morphine to treat chronic pain. The short-acting formulation is usually combined with aspirin or acetaminophen.

Oxymorphone

By mouth: About 4 hours

Controlled-release form by mouth: 12 hours

By intravenous or intramuscular injection: About 6 hours

By rectal suppository: 4 to 6 hours

Oxymorphone can be used instead of morphine to treat chronic pain.

Pentazocine

By mouth: 3 to 4 hours

By intravenous or intramuscular injection: 3 to 4 hours

Pentazocine can block the pain-relieving action of other opioids. It is about as strong as codeine. The usefulness of pentazocine is limited because higher doses do not provide more pain relief and because the drug can cause confusion and anxiety, especially in older people. It is not a good choice for older people.

Tapentadol

Short-acting form by mouth: 3 to 6 hours

Long-acting form by mouth: 12 hours

Tapentadol is used to treat neuropathic pain due to diabetes, as well as moderate to severe acute pain and moderate to severe chronic pain.

Tramadol

Short-acting form by mouth: 4 to 11 hours

Long-acting form by mouth: 12 to 24 hours

With tramadol, the potential for abuse is less than that with other opioids. It is not as potent as other opioid analgesics.