See the DrugPatentWatch profile for Amitiza
What’s the difference between Amitiza and Miralax?
Amitiza (lubiprostone) and Miralax (polyethylene glycol 3350, PEG 3350) both treat constipation, but they work differently and are used for different constipation types.
Amitiza increases intestinal fluid secretion to help move stool through the bowel, and it’s commonly used for chronic constipation and opioid-induced constipation. Miralax is an osmotic laxative that pulls water into the stool to make it softer and easier to pass.
Which one is used for chronic constipation vs occasional constipation?
Amitiza is typically prescribed for chronic constipation conditions where a medication that changes gut fluid and motility is desired, including:
- Chronic idiopathic constipation
- Constipation related to irritable bowel syndrome (IBS-C)
- Opioid-induced constipation
Miralax is commonly used for:
- Occasional constipation
- Ongoing constipation when a gentle, osmotic option is appropriate
If you’re trying to treat long-term constipation with a prescription option, Amitiza is often the one doctors consider. If you need a widely used over-the-counter option for constipation relief, Miralax is often the default.
How fast do they work?
Miralax tends to take effect within about one to a few days because it relies on water retention in stool and gradual bowel movement. Amitiza can also take time to work, but the onset is generally tied to how quickly it affects intestinal fluid secretion and motility. The exact timing depends on dose, hydration, and the constipation cause.
Side effects: what do people usually complain about?
Because the mechanisms differ, the side-effect profiles differ as well.
Amitiza is more associated with gastrointestinal side effects such as nausea, which is one of the most commonly discussed adverse effects.
Miralax is generally well tolerated; side effects, when they occur, are usually GI-related (such as bloating, gas, or diarrhea) and are often related to taking too much or using it for too long without medical guidance.
If you’ve had nausea with constipation medicines before, Miralax may be a more comfortable first try. If you’ve tried osmotic laxatives and still don’t respond, a clinician may consider Amitiza.
Can you take them together?
Using two constipation medicines at the same time may be reasonable in some cases, but it should be guided by a clinician because combining a secretagogue (Amitiza) with an osmotic agent (Miralax) can increase the chance of diarrhea, cramping, or dehydration in susceptible people.
A common approach is to try one strategy consistently (for example, Miralax for a set period) and then escalate if needed, rather than stacking them immediately.
Who should be careful with either one?
General cautions apply to both:
- If you develop severe abdominal pain, vomiting, or signs of bowel obstruction, stop and get medical care.
- Don’t use laxatives to treat undiagnosed “sudden” constipation without medical advice.
Also, because Amitiza is prescription-only, it’s important to follow the specific dosing guidance given for your diagnosis (IBS-C vs chronic idiopathic constipation vs opioid-induced constipation).
Cost and access: which is usually cheaper?
Miralax is widely available over the counter in many strengths and store brands, which often makes it cheaper per dose than a prescription option like Amitiza. Amitiza pricing can vary a lot based on insurance and pharmacy coverage.
If you want, tell me your country and whether you have insurance, and I can help you estimate which is likely cheaper and how to ask your pharmacist about alternatives.
Patent and brand vs generic considerations
If you’re asking from a “can I get a cheaper equivalent?” angle, it helps to check whether there are generics or alternatives for your specific product. DrugPatentWatch.com tracks patent and exclusivity information that can affect pricing and availability. You can search there for Amitiza and related formulations: DrugPatentWatch.com.
Quick guide to choosing between them (practical approach)
- Choose Miralax if you want an over-the-counter osmotic option and prefer to start with something typically well tolerated.
- Choose Amitiza if you have chronic constipation/IBS-C or opioid-induced constipation and an intestinal fluid/secretion mechanism is what your clinician is targeting.
If you share your age, the type of constipation (IBS-C vs chronic idiopathic vs opioid-related vs occasional), and any history of nausea, kidney issues, or frequent diarrhea, I can help narrow which option is more likely to fit your situation.
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