Kristalose is a prescription laxative that comes as a powder you dissolve in water before drinking. Its active ingredient is lactulose, a synthetic sugar that your body can’t digest, which works by drawing water into the colon to soften stool and stimulate bowel movements. It’s FDA-approved for the treatment of chronic constipation in adults.
How Kristalose Works
Lactulose, the active ingredient in Kristalose, is classified as a colonic acidifier. Unlike regular sugars, it passes through your stomach and small intestine completely undigested. When it reaches the colon, bacteria ferment it into acids that pull water into the bowel. This extra fluid softens stool and increases its volume, which triggers the natural contractions that move things along.
Because it relies on bacterial fermentation in the colon rather than chemical stimulation of the intestinal wall, lactulose is considered a gentler type of laxative. It doesn’t work instantly. Most people need 24 to 48 hours before noticing results, and it can take a few days of consistent use to establish a regular pattern.
What Makes It Different From Liquid Lactulose
Lactulose has been available as a thick, sweet syrup for decades. Kristalose is the same drug in a different form: dry crystals packaged in single-dose packets that you mix into a beverage. The distinction matters more than it sounds, because taste and consistency are major reasons people stop taking lactulose.
In a study comparing the two forms in adults with chronic constipation, 44% more patients preferred the taste of the powder over the liquid, and 57% more preferred its consistency. Portability was an even bigger gap: more than six times as many patients preferred the powder’s convenience. Overall, 77% more patients chose the powder form when given the option. For people who need to take lactulose long-term, that preference can be the difference between sticking with the medication and quietly abandoning it.
This is especially relevant for patients with liver disease who require large daily doses of lactulose (sometimes more than 50 mL of syrup per day). Many of those patients struggle to swallow or keep down that volume of thick, sugary liquid, leading to poor compliance. The powder form dissolves into a much more tolerable drink.
Dosage and Preparation
Kristalose comes in single-dose packets of 10 grams or 20 grams. The usual adult dose is 10 to 20 grams daily, though a prescriber can increase it to 40 grams per day if needed. You dissolve the contents of a packet in at least 4 ounces of water or another beverage, stir until the crystals are fully dissolved, and drink it. There’s no need to refrigerate unopened packets, which adds to the portability advantage over the liquid version.
Common Side Effects
The side effects of Kristalose are almost entirely digestive, which makes sense given how it works. Gas and bloating are the most frequently reported issues. The bacterial fermentation that makes lactulose effective also produces gas as a byproduct, so flatulence and a feeling of abdominal fullness are common, particularly in the first few days of use.
Other reported side effects include abdominal cramps, belching, nausea, and vomiting. Taking too much can cause diarrhea, which is essentially the mechanism working too aggressively. If loose stools become persistent, the dose is usually too high. These effects tend to be mild and often improve as your body adjusts over the first week or so.
Who Should Not Take It
Kristalose is contraindicated for anyone with galactosemia, a rare inherited metabolic disorder in which the body cannot break down a sugar called galactose. Since lactulose is a synthetic sugar made from galactose and fructose, taking it would cause galactose to accumulate in the blood and tissues, where it gets converted into a toxic alcohol derivative that can damage organs. People on a low-galactose diet for any reason should also avoid it.
Because lactulose can affect blood sugar levels to a small degree, people with diabetes should be aware that it contains small amounts of free sugars. It’s also worth noting that long-term or high-dose use can cause electrolyte imbalances, particularly low potassium, so periodic blood work may be appropriate for people who take it continuously.
How Well It Works
In a randomized, double-blind trial of 30 elderly men with chronic constipation, patients taking lactulose averaged about 7 bowel movements per week and had bowel movements on roughly 5.3 days per week. That’s a meaningful improvement for people who were previously struggling with regularity. The study compared lactulose to sorbitol (another osmotic laxative) and found no significant difference in effectiveness between the two, with patient preferences split almost evenly.
Lactulose is not the fastest-acting option for constipation. Stimulant laxatives work within hours, while lactulose typically takes a day or two. Its value is in daily, ongoing use for chronic constipation rather than occasional acute relief. For people who need a laxative they can take regularly without worrying about dependency or harsh cramping, lactulose fills a specific role that stronger options don’t.