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Relistor (Methylnaltrexone)

Prescription medicineOnly Available By Prescription

Top brand choice

Strength Pack Size Qty
12mg/0.6ml (vial)
Pack Size

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Example: If you find a product on Canada Drugs Direct for $50.00 and find the same product for $40.00 at another mail order pharmacy, we will provide you with a $12.50 discount, bringing your total to $37.50.

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  • We will only match the current advertised price.
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What is a Generic Drug?

A generic drug is a copy of the brand-name drug with the same dosage, safety, strength, quality, consumption method, performance, and intended use. Before generics become available on the market, the generic company must prove it has the same active ingredients as the brand-name drug and works in the same way and in the same amount of time in the body.

The only differences between generics and their brand-name counterparts is that generics are less expensive and may look slightly different (eg. different shape or color), as trademarks laws prevent a generic from looking exactly like the brand-name drug.

Generics are less expensive because generic manufacturers don't have to invest large sums of money to develop a drug. When the brand-name patent expires, generic companies can manufacture a copy of the brand-name and sell it at a substantial discount.


Relistor (Methylnaltrexone) is a medication that is part of a group of drugs called opioid antagonists. It works by blocking the opioid receptors in the intestines, which helps alleviate constipation caused by opioid pain medications. This drug is specifically developed for people experiencing constipation due to long-term opioid use for pain management, including those with chronic non-cancer pain and those with cancer who no longer require weekly increases in opioid dosage.

Fact Table






Low bioavailability

Legal status


Chemical Name


Elimination half-life

8 hours

Dosage (Strength)

12mg / 0.6ml (vial)


Consult Doctor



Protein binding


PubChem CID





Not Available

ATC code





Not Available

Routes of administration



The suggested dose for Relistor injections in adults living with chronic non-cancer pain-related constipation is a single 12 mg daily dose. For adults with advanced illness accompanied by opioid-induced constipation, the dosage varies depending on weight: For those under 38 kg, a daily dosage of 0.15 mg/kg is recommended; for individuals weighing from 38 kg up to 62 kg, an 8 mg daily dose is recommended; for those between 62 kg and 114 kg, the suggested dose is 12 mg daily; and for those more than 114 kg, a daily dosage of 0.15 mg/kg is prescribed.

Always follow the instructions provided by your medical professional and seek further clarification if needed. Before administering the injection, ensure the targeted skin area is both clean and visibly free from infection. Injections can be administered into the thigh, upper arm, or abdominal region.


The active ingredient in Relistor is methylnaltrexone bromide.


Avoid taking or using Relistor if any of the following apply:


  • Before taking Relistor, it is important to inform your doctor about:
    • Any medications you take, to prevent possible interactions
    • Any medical conditions you have, such as liver or kidney disease which might require a dosage adjustment
    • If you are pregnant or breastfeeding
    • If you plan to become pregnant or breastfeed
  • Exercise caution if you're already aware of or suspect gastrointestinal issues; the use of Relistor could pose risks. In case of persistent or worsening stomach pain, discontinue the medication and seek immediate medical help.
  • In instances of ongoing or severe diarrhea while on this medication, discontinuation of Relistor and consultation with your healthcare provider is recommended.
  • For those with a compromised blood-brain barrier, weigh the pros and cons before using Relistor with a healthcare provider. Watch for signs of opioid withdrawal, including restlessness, nausea, or anxiousness, and reach out to your healthcare provider if needed.
  • Ensure you have easy access to a bathroom facility when taking the medication.
  • Stop taking Relistor if your healthcare provider discontinues opioid pain treatment.
  • If your history of opioid use is less than a month, you may find the effectiveness of Relistor to be reduced.
  • Before starting Relistor, it is advised to stop any regular laxative use. If Relistor doesn't provide the expected results within three days, you may consider restarting laxative use.
  • Should your opioid medication regimen change, reconsider the need for ongoing Relistor use with a healthcare provider.
  • Routine healthcare provider check-ups are recommended to monitor the drug’s efficacy and possible adverse effects.

Side Effects

While Relistor can provide relief for patients, there are certain side effects that individuals should be aware of before beginning treatment. The most common side effects of Relistor include:

  • Diarrhea
  • Headache
  • Sweating
  • Anxiety
  • Muscle spasms
  • Pain in the stomach area
  • Chills
  • Runny nose

Relistor may also cause severe side effects, including:

  • Digestive Tract Complications: Severe pain in the abdominal area may be a sign of a serious issue like a gastrointestinal perforation. If you experience persistent or escalating severe stomach pain, discontinue the medication and seek immediate medical attention.
  • Persistent or Intense Diarrhea: If you experience persistent or severe diarrhea, it's important to stop using Relistor and consult a healthcare professional.
  • Symptoms of Opioid Withdrawal: While on this medication, you may experience withdrawal symptoms like excessive sweating, diarrhea, abdominal pain, nervousness, and chills. If you experience any of these symptoms, contact your healthcare provider.

This is not an exhaustive list of side effects. If you experience any side effects, consult a healthcare provider for proper advice and management.


  1. Relistor (Methylnaltrexone) Prescribing Information. Bridgewater, NJ: Salix Pharmaceuticals; 2018.

IMPORTANT NOTE: The above information is intended to increase awareness of health information and does not suggest treatment or diagnosis. This information is not a substitute for individual medical attention and should not be construed to indicate that use of the drug is safe, appropriate, or effective for you. See your health care professional for medical advice and treatment.

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