Relistor is expensive because it’s a specialty drug with no generic alternative, patent protection lasting until at least 2030, and a narrow patient population that limits competitive pressure on pricing. A single injection dose averages around $175, and the tablet form carries similarly high monthly costs. Several overlapping factors keep the price elevated.
It Works Differently Than Regular Laxatives
Relistor isn’t just another laxative. It belongs to a small class of drugs designed specifically to treat constipation caused by opioid medications. When opioids bind to receptors lining the digestive tract, they slow everything down, making stool hard and difficult to move. Standard laxatives try to soften stool or stimulate gut movement, but they don’t address this underlying mechanism. For many patients on long-term opioids, regular laxatives simply don’t work well enough.
Relistor blocks opioid receptors in the gut without crossing into the brain, which means it reverses the constipating effects of opioids without interfering with pain relief or triggering withdrawal. That selectivity is what makes the drug clinically valuable, and it’s also what makes it expensive to develop and manufacture. You’re paying for a precisely engineered molecule, not a bulk compound that’s been on the market for decades.
Patent Protection Blocks Generic Competition
The single biggest driver of Relistor’s price is the absence of a generic version. FDA records show that Relistor’s injectable forms are protected by patents expiring on December 31, 2030, while the tablet form has patent protection until March 10, 2031. Although at least one generic manufacturer has filed an application for each formulation, none have reached the market yet.
Until those patents expire or a generic gains approval, Salix Pharmaceuticals (the current marketer) faces no direct price competition for methylnaltrexone. That kind of exclusivity is the primary reason any brand-name drug stays expensive. Once generics do enter the market, prices typically drop by 80% or more within a few years. But for now, Relistor patients are likely looking at brand-name pricing through at least 2030.
A Small Market Means Higher Per-Patient Costs
Relistor treats a relatively narrow group of patients: people on chronic opioids whose constipation hasn’t responded to cheaper treatments. The drug was originally granted an orphan drug designation in 1996 for opioid-induced constipation unresponsive to conventional therapy, though that designation was later withdrawn and the drug was never approved under orphan drug status. Still, the patient population remains limited compared to blockbuster drugs prescribed to millions.
Pharmaceutical companies spread their research, manufacturing, and regulatory costs across the number of people who will use the drug. A smaller market means each patient absorbs a larger share of those fixed costs. Relistor went through years of development, multiple clinical trials, and FDA review for both its injectable and oral forms. All of that investment gets recouped from a comparatively small pool of prescriptions.
Even Competitors Are Expensive
Relistor isn’t uniquely overpriced within its drug class. The two other drugs that work by the same mechanism carry similar costs. Movantik (naloxegol) runs roughly $435 for a 30-day supply, and Symproic (naldemedine) averages about $483 for 30 tablets. With Relistor’s injectable form costing around $175 per dose and multiple doses needed per month, monthly costs across all three drugs land in a similar range.
When every competitor in a drug class is expensive, there’s little market incentive for any manufacturer to lower prices significantly. All three target the same small patient population, all are still under patent, and all require a prescription. This lack of meaningful price competition within the class keeps costs high across the board.
Insurance Hurdles Add to the Burden
Most insurers treat Relistor as a non-preferred specialty drug, which means prior authorization is required before coverage kicks in. The approval criteria are strict. A typical example from North Carolina’s Medicaid program illustrates what patients face: you must have been on opioids for at least four weeks, you need a confirmed diagnosis of opioid-induced constipation, and you must have already tried and failed (or be unable to tolerate) both Amitiza and Movantik before Relistor will be covered. Initial approval lasts only four months, after which your provider must submit documentation showing your symptoms have improved to get coverage renewed for up to 12 months.
These requirements exist precisely because the drug is so costly. Insurers want to ensure cheaper alternatives have been exhausted first. But the process also means delays, paperwork, and sometimes denials that leave patients paying out of pocket or going without the medication entirely.
Limited Help With Out-of-Pocket Costs
Salix Pharmaceuticals offers a copay savings program, but it’s only available to patients with commercial (private) insurance. If you’re on Medicare, Medicaid, TRICARE, Veterans Administration coverage, or any other government health plan, you’re excluded from the program entirely. That rules out a large portion of the people who actually take Relistor, since many chronic opioid users are older adults on Medicare or patients covered by government programs.
For those who do qualify, the copay card can reduce out-of-pocket costs at the pharmacy. But it doesn’t change the drug’s list price, and it doesn’t help uninsured patients or anyone on government insurance. Independent patient assistance foundations sometimes offer additional support, but availability varies and funding can run out.
What This Means for Your Costs
If you’re facing a Relistor prescription, the realistic picture is this: expect your insurer to require you to try other treatments first, expect prior authorization paperwork, and expect significant cost even with coverage. The injectable form at $175 per dose adds up quickly if you need it several times a week. The tablet form’s monthly cost is comparable to its competitors in the $400 to $500 range.
Your best leverage points are working with your prescriber to document failed trials of cheaper alternatives (which speeds up prior authorization), checking eligibility for the manufacturer’s copay program if you have commercial insurance, and asking your pharmacy to run a price comparison across formulations. The injectable single-dose vial, prefilled syringe, and oral tablet may be priced differently depending on your specific plan. Generic competition likely won’t arrive before 2031 at the earliest, so the current pricing landscape is unlikely to shift meaningfully in the near term.