Naltrexone (Vivitrol) vs. Naloxone (Narcan): How Are These Opioid Blockers Different?

Naltrexone and naloxone sound very similar, and they both reverse the effects of opioids.

However, these two medications are quite different. Naltrexone, brand name Vivitrol, is a medication that is FDA-approved to treat alcohol use disorder and opioid use disorder. Naltrexone is used as part of a treatment plan extending over weeks to months.

Naloxone, brand name Narcan, quickly blocks the effects of opioids, including ones that can be fatal. It is fast-acting, but its effects do not last long. Naloxone buys time to get someone who has overdosed on opioids to an emergency room for further treatment.

Opioid use is common. According to a 2021 SAMHSA survey, 9.2 million people misused opioids in the survey year. About 16.5% of the population (46 million people) meet the criteria for having a substance use disorder. Of these, about half misuse alcohol, and the other half misuse drugs.

Opioids can cause physical dependence and addiction and have a high potential for overdose. In 2021, over 100,000 people died from an overdose. Almost three in every four deaths involved synthetic opioids.

Examples of opioids include heroin, fentanyl, oxycodone, hydrocodone, codeine, and morphine.

What Is Naloxone? 

Naloxone is a medication that reverses the effects of opioids. Since opioid drugs can slow respiration and impair consciousness, naloxone is a lifesaving medication when it is given quickly.

Narcan (naloxone) does not require a prescription. In fact, many schools, colleges, restaurants, and other public spaces dispense Narcan to treat opioid overdoses.

Naloxone can be administered as an injection or a nasal spray.

Because naloxone must be given quickly, there has been a push to make it readily available in many public spaces and to train people on how to administer it.

Naloxone does not cause harm if a person has another medical condition that is mistaken for an opioid overdose, such as a heart attack or diabetic coma. Administering naloxone can save a person’s life, even if you are not sure whether they overdosed on opioids.

Signs of an opioid overdose include:

• Being unconscious
• Having shallow or undetectable breathing
• Being limp
• Having a slow or irregular heartbeat
• Having a bluish tinge to lips, tongue, or fingertips

After receiving naloxone, a person who has overdosed on opioids will begin to arouse and recover. It is important to call for emergency help because naloxone is short-acting.

How Naloxone Works

Naloxone can reverse the effects of opioids. Naloxone binds to opioid receptors in the brain and throughout the body more tightly than opioid drugs.

When naloxone is given to someone who has taken an opioid, naloxone displaces opioid drugs from their receptors and reverses their effects.

This is lifesaving because opioids can slow your breathing to where it is life-threatening and cause you to become unconscious.

What Is Naltrexone? 

Naltrexone is FDA-approved to treat opioid use disorder and alcohol use disorder. It is only available by prescription obtained through an in-person or online medical appointment.

Naltrexone is a versatile medication. Besides treating substance use disorders, naltrexone can be prescribed in a very low dose to treat chronic pain or inflammation. Researchers are still working to understand the many ways low-dose naltrexone can be used to improve health and treat disease.

Naltrexone can also be combined with other medications. For example, naltrexone/bupropion is a combination medication that induces weight loss better than either medication can on its own.

How Naltrexone Works

Naltrexone also binds to opioid receptors in the brain. By blocking these receptors for extended periods, naltrexone can reduce the pleasure and reward people get from using opioids, alcohol, or consuming highly palatable foods.

When you drink alcohol, use opioids, or consume highly palatable foods, your brain releases dopamine, a chemical messenger. Dopamine reinforces that these are all pleasurable activities. Increased dopamine release makes you crave these substances.

Over time, excessive alcohol and opioid use changes your brain’s sensitivity to natural opioids and dopamine. This can cause physical dependence and addiction.

Naltrexone blocks opioid receptors, which decreases the amount of natural opioids and dopamine your brain produces. Because your brain does not get the same burst of pleasure, your cravings subside.

Two key areas of the brain, the hypothalamus and the reward pathway, control appetite and cravings. Naltrexone/bupropion binds to receptors here, reducing food cravings and hunger and increasing satiety with eating. Naltrexone/bupropion is one of six FDA-approved medications for weight loss.

Ways Naloxone & Naltrexone Differ

Naloxone and naltrexone are both FDA-approved medications that help people who take opioids. Naloxone can rescue a person from an opioid overdose. Naltrexone is used after a person stops using opioids to prevent a relapse.

Naloxone is available by prescription and over the counter. It is easy to administer and does not cause harm, even if the cause of decreased respirations and alertness is not an opioid overdose.

Naloxone is designed to be administered quickly. It is short-acting, and treatment must be followed by emergency care. Once naloxone is metabolized in the body, opioids can continue to have their effect.

Anyone can administer naloxone to someone in need and potentially save their life.

Naltrexone is a prescription medication that can be prescribed in many forms, including:

• At a higher dose to treat alcohol use disorder and opioid use disorder.
• At a lower dose to improve pain and reduce inflammation, among other things.
• Combined with bupropion to treat obesity and induce weight loss.

Naltrexone is longer-acting and more likely to cause side effects and have drug interactions than naloxone. Be sure to supply your doctor and pharmacist with your complete medical history so they can check to see if you are at increased risk for any naltrexone side effects.

People who request a prescription for naltrexone can have many motivations. For example, naltrexone/bupropion is frequently prescribed to assist with weight loss as part of a more comprehensive lifestyle treatment plan. 

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