Alternatives to Lactulose If You Can't Fill Your Prescription

Lactulose has two very different uses: treating chronic constipation and managing hepatic encephalopathy (HE), a brain condition caused by liver disease. The right alternative depends entirely on why you're taking lactulose. Always consult your doctor before switching — especially if you're being treated for HE, where medication changes can carry real risk.

Alternatives to Lactulose for Constipation

If you take lactulose for chronic constipation and can't find it at your pharmacy, several effective alternatives exist — many available over the counter:

1. Polyethylene Glycol (PEG / MiraLax)

PEG 3350 (sold as MiraLax and generics) is widely considered the best alternative to lactulose for constipation. It's an osmotic laxative that works by the same mechanism — drawing water into the colon. Studies show PEG is actually more effective than lactulose with less flatulence and bloating. It's available over the counter, inexpensive (often under $15 for a 30-day supply), and tasteless when dissolved in liquid.

Typical dose: 17 g (one capful) dissolved in 8 oz of liquid once daily. Safe for long-term use.

2. Senna (Senokot, Ex-Lax)

Senna is a stimulant laxative derived from the senna plant. Unlike lactulose, which softens stool by osmotic action, senna directly stimulates intestinal muscle contractions. It works faster (6–12 hours vs. 24–48 hours for lactulose) and is available OTC. It's commonly used short-term for constipation but is appropriate for longer use in some patients (such as those on chronic opioid therapy).

3. Docusate Sodium (Colace)

Docusate is a stool softener rather than a true laxative. It helps water penetrate the stool, making it easier to pass — but it doesn't stimulate a bowel movement the way lactulose or senna does. It's gentle and well-tolerated but generally not sufficient for patients with significant constipation.

4. Psyllium (Metamucil)

Psyllium is a bulk-forming fiber laxative. It absorbs water in the gut to form a thick gel, which eases stool passage. It's an excellent long-term option and also benefits cholesterol levels. However, it must be taken with adequate water to avoid worsening constipation and is not ideal for patients with active GI motility issues.

Alternatives to Lactulose for Hepatic Encephalopathy (HE)

This is more medically complex. Lactulose is the standard of care for preventing and treating HE in patients with liver disease. Do not substitute without direct guidance from your hepatologist or gastroenterologist. That said, several options have clinical evidence:

1. Rifaximin (Xifaxan)

Rifaximin 550 mg twice daily is used alongside lactulose (or instead of it when lactulose is not tolerated) to reduce ammonia production by gut bacteria. Multiple guidelines, including AASLD/EASL, support rifaximin as an alternative or add-on. It's better tolerated than lactulose but significantly more expensive — often requiring prior authorization from insurance.

2. Polyethylene Glycol (PEG) for Acute HE

Studies including the HELP randomized clinical trial show that PEG leads to faster HE resolution than lactulose in hospitalized patients with acute HE. PEG can be considered an alternative or adjunct therapy for acute HE, particularly when rapid catharsis is needed. It's generally reserved for inpatient use.

3. Lactitol

Lactitol is another non-absorbable disaccharide similar to lactulose that works by the same mechanism. It's used widely in Europe and some other countries as a direct substitute for lactulose in HE treatment. Meta-analyses suggest comparable efficacy with potentially better taste. Lactitol is not widely available in the United States, but your provider may be able to source it through specialty channels.

How to Talk to Your Doctor About Switching

When you call your provider, have these details ready:

• Your current lactulose dose and formulation
• Why you're taking it (constipation vs. HE)
• How long you've been unable to find it
• Whether you've tried multiple pharmacies or mail-order

Before giving up on lactulose entirely, try using the tools in our guide on how to find lactulose in stock near you. In most cases, it's available — just not at every pharmacy.

Quick Comparison Table

For Constipation: PEG/MiraLax (OTC, best evidence), Senna (OTC, faster onset), Psyllium (OTC, fiber-based), Docusate (OTC, gentle).

For Hepatic Encephalopathy: Rifaximin 550 mg BID (Rx, well-tolerated), PEG (for acute inpatient HE), Lactitol (not widely available in US). Always consult your hepatologist before substituting.