Opioid Agonist

An opioid agonist is an opioid that activates some or all of the opioid receptors in the brain. Opioid agonists can either be full opioid agonist or partial opioid agonist.

  • Full opioid agonists are those drugs which activate the opioid receptors in the brain fully. These are the drugs that people take in order to relieve pain or get high.
  • Partial opioid agonists are those drugs which do activate the opioid receptors in the brain but to a much lesser degree than full opioid agonists. These are often used to treat opioid addiction and in opioid detox.

Opioid agonists are most types of opioid drugs that people are prescribed by their doctors. Street drugs like heroin and opium are also opioid agonists. They are also called narcotics or just opioids. Opioid antagonists are separate and they work by blocking the euphoric and pain killing effects of opioid agonists of binding to opioid receptors as they have “structural similarity to narcotics themselves” (NIDA Archives).

To learn more about opioid agonists, call 800-821-3880.

How Do Opioid Agonists Work?

The NIDA states, “Opioids act by attaching to specific proteins called opioid receptors, which are found in the brain, spinal cord, gastrointestinal tract, and other organs in the body.” Once they have attached to these receptors, they create certain biochemical reactions which result in the effects of opioids, such as:

Opioid Agonist

Euphoria and fatigue are common side effects of an opioid agonist.

  • Euphoria
  • Insensitivity to pain
  • Drowsiness
  • Fatigue
  • Constipation
  • Nausea

“When the drugs attach to certain opioid receptors, they block the transmission of pain messages to the brain” (ISATE). They also cause euphoria by “affecting the brain regions that mediate pleasure.” They can relieve stress and also cause people to feel comfortable and relaxed because of the effect they have on the brain.

Full Opioid Agonists

Full opioid agonists are the more intense opioid agonists. They are the ones that are prescribed to patients and the drugs that opioid addicts take to get high. The UIC states that there are strong agonists and moderate agonists which are all still considered to be full opioid agonists.

Strong opioid agonists are:

  • Morphine
    Morphine is a drug that has been prescribed to treat moderate to severe pain for many years. Often, people abuse it in order to get high. It is usually used by those who are already addicted to opioids, and according to the NLM, it “should only be taken by people who are tolerant (used to the effects of the medication) to opioid medications.”
  • Meperidine
    Meperidine is the opioid agonist that is better known by its brand name Demerol. It has a strong effect on pain patients and should be prescribed to those with moderate to severe pain. Some of the street names used for meperidine are D, demmies, and pethidine.
  • Fentanyl
    Fentanyl is another medication that should not usually be prescribed to patients who are not already tolerant to the effects of opioid medications. Fentanyl is a strong opioid agonist that is often abused by addicts. Some of its street names are China white, murder 8, and TNT.

Heroin is also a strong opioid agonist. It only lasts about two hours when in a person’s system, but it has “no acceptable medical value” in the United States (UIC). Heroin is one of the most dangerous opioids and also the most commonly abused.

Moderate opioid agonists include:

  • Oxycodone
    Oxycodone is a moderate opioid agonist, meaning that its effects are not as strong as fentanyl or morphine. It is often prescribed to patients with pain issues on a take-as-needed basis. People still abuse oxycodone though at high doses in order to feel the euphoric high.
  • Codeine
    Codeine is often abused by opioid addicts when they cannot find any other opioid medications. It can be found in cough syrup as a cough suppressant and it can also be prescribed to patients for pain.

Types of Opioids

Partial Opioid Agonists

There is also a kind of opioid drug called a partial opioid agonist. According to SAMHSA, this means that a drug “is an opioid, and thus can produce typical opioid agonist effects and side effects such as euphoria and respiratory depression” and also that “its maximal effects are less than those of full agonists.” Given that their effects are not as strong but that they still act as opioids do on the brain, they are very beneficial for those who are fighting opioid addiction and attending opioid detox. One of the most beneficial drugs used for this purpose is buprenorphine.


Burprenorphine is a “mixed agonist-antagonist,” according to UIC, and it produces agonist effects on some receptors and antagonist effects on others. It is actually very good for those who have been struggling with opioid addiction.

The NLM states that buprenorphine can “prevent withdrawal symptoms when someone stops taking opioid drugs by producing similar effects to these drugs,” almost acting as a placeholder that allows the person to curb withdrawal symptoms and cravings while not taking opioids that harm him or her.

There are two types of brand name medications that contain buprenorphine:

  • Subutex
  • Suboxone

Subutex is buprenorphine alone and Suboxone contains buprenorphine and naloxone. Suboxone is often prescribed to opioid addicts because the two drugs used together can create a stronger foundation for recovery in the patient. Buprenorphine or naloxone and buprenorphine together can “precipitate withdrawal” symptoms in the person who injects the drug or crushes and snorts it (SAMHSA). This goes a long way toward preventing abuse of buprenorphine drugs.

The side effects of buprenorphine are:

  • Headache
  • Constipation
  • Vomiting
  • Insomnia
  • Sweating
  • Stomach pain

These side effects are fairly similar to those caused by other opioid agonists so addicts will usually be familiar with them already. The drug is very beneficial to patients and does not have the same issues that opioid agonist treatment medications like naltrexone do.

Opioid agonists can be any opioid drugs that attach to opioid receptors in the brain. As there are different levels of opioid agonists, they are used for different effects. Using opioid agonists should always be done under the care and supervision of a doctor, and the patient should not deviate from his or her dosage.

If you abuse opioid agonists and want help finding treatment, call 800-821-3880 to speak with an addiction specialist. 

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