Comprehensive medication guide to Lactulose including estimated pricing, availability information, side effects, and how to find it in stock at your local pharmacy.
Estimated Insurance Pricing
$0–$15 copay for generic lactulose on most commercial insurance plans (Tier 1–2). Medicare Part D typically $0–$10 per fill. Medicaid coverage available in most states with minimal or no copay. Kristalose brand may require prior authorization.
Estimated Cash Pricing
$15–$65 retail for generic lactulose solution (473 mL / 30-day supply); as low as $4–$13 with GoodRx or SingleCare coupons. Kristalose brand: ~$385 retail, reduced to ~$108 with GoodRx or as low as $5 with Cumberland manufacturer coupon.
Medfinder Findability Score
88/100
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Lactulose is a synthetic sugar — a disaccharide made from galactose and fructose — used as a prescription laxative in the United States. It has been used medically since 1966 and received FDA approval in 1977. With over 900,000 prescriptions filled in 2023, it is one of the most commonly prescribed laxative medications in the country.
Lactulose is FDA-approved for two primary indications: chronic constipation (Kristalose powder form) and prevention and treatment of portal-systemic (hepatic) encephalopathy — a brain condition that occurs when the liver cannot filter toxins like ammonia from the blood. It appears on the World Health Organization's List of Essential Medicines.
Lactulose is available as a generic oral solution (10 g/15 mL), as Kristalose brand crystalline powder packets (10 g and 20 g), and as a rectal formulation for hospital use. It is not a controlled substance, and any licensed prescriber can write a lactulose prescription.
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The human small intestine cannot digest lactulose — it lacks the enzymes to break the molecule apart. As a result, lactulose passes through the stomach and small intestine unchanged and arrives intact in the colon. This non-absorbable nature is precisely what makes lactulose effective.
For constipation, lactulose works by osmosis — its presence draws water from surrounding tissues into the colon, softening stool. Colonic bacteria then ferment lactulose into lactic, acetic, and formic acids, which lower the pH and further stimulate bowel contractions. The result is a soft, easier-to-pass stool within 24–48 hours.
For hepatic encephalopathy, lactulose reduces blood ammonia through three mechanisms: (1) acidification of the colon converts absorbable ammonia (NH3) to non-absorbable ammonium ion (NH4+), trapping it in the gut; (2) colonic bacteria consume ammonia as a nitrogen source during fermentation; and (3) the laxative effect reduces gut transit time, limiting ammonia production and absorption. This can reduce blood ammonia concentrations by 25–50%.
10 g/15 mL — Oral solution (syrup)
Standard generic formulation. Available in 237 mL, 473 mL, and 946 mL bottles. For constipation: 15–30 mL once daily. For HE: 30–45 mL 3–4 times daily.
10 g per packet — Powder for oral solution (Kristalose)
Brand-name powder packet. Dissolve in 4 oz water. Equivalent to 15 mL of lactulose solution.
20 g per packet — Powder for oral solution (Kristalose)
Brand-name powder packet. Dissolve in 4 oz water. Equivalent to 30 mL of lactulose solution.
10 g/15 mL — Rectal liquid
Used in hospital settings for acute hepatic encephalopathy. 300 mL (200 g) in 700 mL water or NS, retained 30–60 minutes every 4–6 hours.
Generic lactulose oral solution is widely available at most retail pharmacies in the United States and is not in a declared national shortage as of 2026. It is manufactured by multiple pharmaceutical companies, providing supply redundancy. Most chain pharmacies — including CVS, Walgreens, Walmart, and Costco — reliably carry it in stock.
However, Kristalose brand powder (10 g and 20 g packets) is a single-source product with no generic equivalent. Availability of Kristalose can be intermittent at smaller retail pharmacies; calling ahead is recommended. Rectal lactulose formulations are primarily available through hospital and specialty pharmacies.
If you're having trouble locating lactulose at local pharmacies, medfinder calls pharmacies near you to find which ones have your prescription in stock — saving you from time-consuming phone searches, especially important for hepatic encephalopathy patients who can't afford gaps in treatment.
Lactulose is not a controlled substance and has no DEA scheduling restrictions. Any licensed prescriber in the United States can write a lactulose prescription. The type of provider most commonly seen depends on the indication:
Telehealth is a convenient option for obtaining a lactulose prescription for chronic constipation. Platforms such as Teladoc, MDLive, and Amazon Clinic can evaluate and prescribe lactulose during a virtual visit, often same-day. For hepatic encephalopathy, telehealth may be used for follow-up care by an established hepatologist or gastroenterologist.
No. Lactulose is not classified as a controlled substance by the Drug Enforcement Administration (DEA) and has no DEA schedule. There are no special prescribing requirements, quantity restrictions, or early refill limitations related to drug scheduling.
Any licensed prescriber — including primary care physicians, nurse practitioners, physician assistants, gastroenterologists, and hepatologists — can write a lactulose prescription without DEA registration for controlled substances. Refills can be authorized as needed without the 30-day supply restrictions that apply to Schedule II medications. Lactulose does require a prescription in the United States, however — it is not available over the counter as it is in many other countries.
The following side effects are common, especially when first starting lactulose. They typically improve within the first 1–2 weeks:
Serious side effects — seek medical attention:
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Polyethylene glycol (PEG/MiraLax)
OTC osmotic laxative with same mechanism but no fermentation. Better tolerated (less gas). Evidence supports faster HE resolution in acute settings. Preferred by ACG for chronic constipation. 17 g once daily.
Rifaximin (Xifaxan)
Non-absorbable antibiotic used alongside or instead of lactulose for hepatic encephalopathy prevention. 550 mg twice daily. AASLD/EASL guidelines support as complement or alternative when lactulose is not tolerated. Significantly more expensive.
Senna (Senokot)
OTC stimulant laxative for constipation. Faster onset (6–12 hours). Appropriate for short-term or opioid-induced constipation. Does not address hepatic encephalopathy.
Lactitol
Similar non-absorbable disaccharide used in Europe. Works by same mechanism as lactulose for HE and constipation. Better taste tolerance. Limited availability in the United States.
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Antacids (aluminum hydroxide, calcium carbonate, sodium bicarbonate)
moderateRaise colonic pH, counteracting lactulose's acidification mechanism. Most clinically significant for hepatic encephalopathy treatment. Monitor and separate doses if possible.
Oral antibiotics (neomycin, cephalexin, azithromycin, ciprofloxacin)
moderateMay eliminate colonic bacteria responsible for fermenting lactulose and converting ammonia. Reduce effectiveness, especially for HE. Monitor closely during antibiotic courses.
Other laxatives (PEG, senna, bisacodyl, docusate, magnesium citrate)
moderateAdditive laxative effects; can mask adequate lactulose dosing in HE. Do not use concurrently without provider guidance.
Loop diuretics (furosemide, bumetanide, ethacrynic acid)
moderateAdditive potassium lowering (hypokalemia risk). Monitor serum electrolytes regularly in patients on both medications.
Warfarin
moderateLactulose may increase anticoagulant effect of warfarin by unclear mechanism. Monitor INR more closely when starting or adjusting lactulose.
Dichlorphenamide (Keveyis)
moderateAdditive potassium lowering and risk of metabolic acidosis. Modify therapy and monitor closely.
Lactulose is one of the most established, affordable, and well-studied prescription laxatives available. It has been in clinical use since 1966, is on the WHO Essential Medicines List, and provides a dual benefit that no OTC laxative can match — treating both constipation and the potentially life-threatening complication of hepatic encephalopathy in liver disease patients.
For most patients, generic lactulose solution is available at any major pharmacy for under $15 with a discount coupon. Patients on Kristalose brand have access to manufacturer coupons that reduce the cost to as little as $5 per month. While mild GI side effects (gas, bloating) are expected at first, they usually improve within 1–2 weeks.
If you're ever having trouble finding lactulose at your local pharmacy, medfinder can locate which pharmacies near you have it in stock — so you never miss a dose.
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