Naltrexone is a medication approved to treat opioid and alcohol use disorder. It is an opioid antagonist that binds with opioid receptors in the brain to block the euphoric effects of other opioids. This action helps reduce cravings so that you can abstain from opioid or alcohol use more easily. Although naltrexone is not classified as a controlled substance, you should only obtain naltrexone through a prescription from a medical professional. To find out if naltrexone treatment may be suitable for your recovery, reach out to your provider.

In-person treatment for opioid or alcohol use disorder may not be possible for everyone. If you are interested in convenient, online medication-assisted treatment (MAT) with naltrexone or Suboxone, contact the professionals at Confidant Health. Our team will conduct a virtual assessment to determine if online MAT is a good fit for you.

How Long Does It Take for Naltrexone to Work?

How long it takes for Naltrexone to work depends on the method of administration. Naltrexone is available as an oral tablet or an intramuscular injection (XR-NTX).

Oral Naltrexone 

Oral naltrexone kicks in faster than the injectable version. The oral tablets absorb quickly and start to block opioids within one hour of use. 

Injectable Naltrexone (XR-NTX)

Injectable naltrexone is provided as an extended-release formula. It takes a bit longer to start working than oral naltrexone, approximately two hours to achieve its peak opioid-blocking effects. 

How Long Do the Effects of Naltrexone Last?

The length of time naltrexone’s opioid-blocking effects last depends on whether you are prescribed oral or injectable naltrexone. 

Oral Naltrexone 

Oral naltrexone is typically prescribed as a once-daily tablet. The most common dosage is one 50 mg tablet daily, with effects that can last 24 to 36 hours. In some cases, your provider may determine that you need a higher dose of naltrexone, either 100 mg or 150 mg. The former will have effects lasting 48 hours, and the latter will last up to 72 hours.

Injectable Naltrexone 

Injectable naltrexone is an extended-release formula that delivers opioid-blocking effects for four weeks. 

Factors That Affect the Effectivity of Naltrexone

Naltrexone treatment can be highly effective, but it isn't necessarily the best treatment option for everyone. Some factors that can affect how effective naltrexone treatment is for you include:

How long ago opioids were last used

Naltrexone treatment should only be administered seven to 10 days after the last use of short-acting opioids and 10 to 14 days after the last use of long-acting opioids. If you take naltrexone too soon after opioid consumption, you can experience precipitated opioid withdrawal symptoms such as headache, nausea, vomiting, abdominal pain, and agitation.

Taking high doses of opioids

Although Naltrexone is effective at blocking the effects of other opioids, that effect can be overridden with high doses of opioids.

Whether naltrexone treatment is paired with therapy

Naltrexone was found to be more effective when paired with coping skills therapy that includes relapse prevention strategies and support for medication compliance.

How Long Does Naltrexone Stay in Your System?

When you receive treatment for opioid or alcohol use disorder, you may have concerns about traces of your naltrexone medication showing up in tests if your employer or another organization requires you to undergo drug or alcohol testing. 

Although the effects of oral naltrexone last for one to two days, traces of your prescription can be detected in your system after the effects have worn off. How long naltrexone stays in your system depends on the type of test:


Naltrexone can only be detected in urine for four to six hours after you take your medication.


A test can detect naltrexone in your saliva up to 24 hours after ingestion.


A blood test will show traces of naltrexone approximately three to four days after your last consumption.

Hair Follicle

Naltrexone can be found in a hair follicle test up to 90 days after use.

Several other factors can also impact how long naltrexone remains in your system:

  • Age

  • Physical activity

  • Hydration

  • Metabolism

  • Weight

  • Overall health

Generally, employers and other entities are looking for traces of alcohol or opioid drugs when administering drug tests. Naltrexone will not appear on these tests unless the test is specifically looking for naltrexone. If you have any concerns about your medication appearing on a mandatory drug test, you may wish to inform the organization beforehand about your treatment. You can also obtain a note from your provider regarding your prescription.

What Time of Day Should You Take Naltrexone?

Although there is no designated time when naltrexone should be administered, your provider may suggest taking your medication at a specific time of day. The primary determining factor for when you should take Naltrexone will be related to the side effects you experience:

  • Anxiety

  • Insomnia

  • Nervousness

  • Drowsiness

  • Fatigue

  • Nausea

  • Upset stomach

If naltrexone makes you feel anxious, wired, or nervous, your provider will likely suggest taking your medication in the morning to prevent sleeplessness. If you experience excessive drowsiness and fatigue, they will probably tell you to take your prescription at night to avoid safety issues with driving or working. If your naltrexone medication upsets your stomach, your provider will recommend taking your tablet with one of your daily meals to alleviate digestive discomfort.

Find Recovery Support with Online Naltrexone Treatment at Confidant Health

The key to managing opioid or alcohol use disorder is finding the best type of treatment for your needs. If you think the convenience of online medication-assisted treatment might be just what you need to help you stay on track, reach out to the professionals at Confidant Health. We offer virtual naltrexone and Suboxone treatment to help manage symptoms and cravings from opioid or alcohol withdrawal. Get started today by scheduling an online assessment.