Relistor (methylnaltrexone bromide) is a prescription medication used to treat opioid-induced constipation (OIC) in adults. It is FDA-approved for two distinct patient groups: people with chronic non-cancer pain who take opioids, and people with advanced illness or active cancer who need opioids for palliative care. It comes as both an oral tablet and a subcutaneous injection.
Why Opioids Cause Constipation
Opioid painkillers relieve pain by binding to receptors in the brain, but those same receptors also line the walls of the gut. When opioids bind to receptors in the digestive tract, they slow down the muscle contractions that move food through your intestines. They also reduce fluid secretion into the bowel. The result is hard, infrequent stools that ordinary laxatives often can’t fully resolve, because the underlying cause is the opioid itself.
This is where Relistor differs from standard laxatives. It belongs to a class of drugs called peripherally acting mu-opioid receptor antagonists, or PAMORAs. The medication blocks opioid receptors specifically in the gut without crossing the blood-brain barrier. That means it relieves constipation without interfering with the pain relief your opioid provides. Your brain still gets the painkilling effect while your digestive system starts working more normally again.
Who Relistor Is Approved For
The FDA has approved Relistor for two groups of adults with opioid-induced constipation:
- Chronic non-cancer pain: This includes people on long-term opioid therapy whose pain is not related to active cancer. It also covers patients with chronic pain related to prior cancer or its treatment, as long as they don’t need frequent opioid dose increases (such as weekly escalations). Both the tablet and injection forms are available for this group.
- Advanced illness or active cancer: Patients receiving palliative care who need ongoing opioid dose escalation can use Relistor as a subcutaneous injection only. The oral tablet is not approved for this group.
How It Is Taken
For chronic non-cancer pain, Relistor is available as a 450 mg oral tablet taken once daily in the morning, or as a 12 mg subcutaneous injection given once daily. Most people who can tolerate oral medication will use the tablet.
For advanced illness, the injection is the only option, and dosing is based on body weight. People between 62 and 114 kg receive a standard 12 mg injection, while those between 38 and 62 kg receive 8 mg. Patients outside those ranges get a weight-based calculation. In this population, the injection is given every other day as needed, with no more than one dose in any 24-hour period. This less frequent schedule reflects the different needs of patients in palliative care settings.
Doses are reduced for people with moderate or severe kidney impairment or severe liver impairment. For the oral tablet, the dose drops from 450 mg to 150 mg in patients with kidney problems. Injection doses are roughly halved in these patients as well.
How Quickly It Works
Clinical trials measured how often patients had a bowel movement within four hours of taking a dose. In a key study of the oral tablet, patients taking Relistor 450 mg had a rescue-free bowel movement within four hours on roughly 27% of dosing days over the first four weeks, compared to about 18% of dosing days on placebo. That difference was statistically significant, though it also highlights that Relistor doesn’t produce a bowel movement after every single dose. Some days it works within hours, other days the effect takes longer or requires additional support.
Common Side Effects
The most frequently reported side effects are gastrointestinal, which makes sense given how the drug works. Abdominal pain, nausea, diarrhea, and gas are the issues patients report most often. These tend to be mild to moderate and are most noticeable in the first days of treatment as the gut starts responding again. For the injection form, reactions at the injection site (redness, soreness, or slight swelling) can also occur.
Important Safety Concerns
Relistor is contraindicated in anyone with a known or suspected gastrointestinal obstruction, or anyone at increased risk of recurrent obstruction. The reason is serious: the drug has been linked to cases of gastrointestinal perforation, a potentially life-threatening tear in the intestinal wall.
This risk is highest in people who already have conditions that weaken the structural integrity of the gut wall, including peptic ulcer disease, diverticular disease, Crohn’s disease, and infiltrative gastrointestinal cancers or peritoneal metastases. If you develop severe, persistent, or worsening abdominal pain while taking Relistor, that is a signal to stop the medication and get medical attention promptly.
Cost and Access
Relistor is a brand-name medication and can be expensive, particularly without insurance. The manufacturer, Bausch Health, offers a patient assistance program for people who do not have insurance coverage for the drug. Eligibility for patients with Medicare Part D is evaluated on a case-by-case basis. You can reach the program by calling 1-833-862-8727. U.S. citizenship or residency is required to qualify.