Does Lactulose Increase Blood Sugar?
Lactulose does not clinically increase blood glucose levels in patients with type 2 diabetes, despite containing small amounts of carbohydrate impurities from the manufacturing process. 1
Evidence from Clinical Studies
The highest quality evidence demonstrates no significant blood glucose elevation with therapeutic lactulose doses:
A 2021 randomized controlled trial in 24 non-insulin-dependent type 2 diabetic patients showed that both 20g and 30g doses of lactulose (crystal and liquid formulations) produced blood glucose curves nearly identical to water, with no significant difference in area under the curve over 180 minutes. 1
The same study found that despite liquid lactulose containing approximately 30% carbohydrate impurities versus ≤3% in crystal formulations, both produced comparable blood glucose responses to water. 1
A 2018 study in healthy volunteers confirmed that 10g and 20g lactulose doses produced no changes in blood glucose levels compared to water, while 20g glucose increased blood glucose by approximately 3 mmol/L (P < 0.0001). 2
Mechanism Explaining Minimal Absorption
The FDA drug label clarifies that lactulose is poorly absorbed systemically:
Lactulose given orally results in only small amounts reaching the blood, with urinary excretion of 3% or less, essentially complete within 24 hours. 3
Lactulose reaches the colon essentially unchanged where it is metabolized by bacteria, rather than being absorbed as glucose in the small intestine. 3
When incubated with human small intestinal mucosa extracts, lactulose was not hydrolyzed during a 24-hour period. 3
Important Clinical Caveat
One isolated case report from 1995 documented marked hyperglycemia when a diabetic patient switched lactulose brands:
A patient with diet-controlled diabetes experienced deterioration in glycemic control requiring insulin when changing lactulose brands, which resolved upon returning to the original brand. 4
This suggests potential variability in carbohydrate impurity content between manufacturers, though this has not been replicated in controlled studies. 4
Guideline Recommendations for Diabetic Patients
The American Diabetes Association recommends monitoring diabetic patients carefully due to lactulose's carbohydrate content, though this appears to be precautionary rather than evidence-based:
Guidelines suggest monitoring may require adjustment in glucose management, though recent clinical trials contradict the need for routine concern. 5
The American Gastroenterological Association recommends starting lactulose at 10-20g (15-30 mL) daily as a single evening dose to minimize side effects, without specific glucose monitoring requirements. 5
Practical Clinical Approach
For diabetic patients requiring lactulose:
Lactulose can be safely prescribed at standard therapeutic doses (15-30 mL daily, up to 60 mL daily maximum) without expectation of clinically significant blood glucose elevation. 5, 1
Routine blood glucose monitoring beyond standard diabetic care is not necessary based on current evidence, though awareness of the 1995 case report suggests vigilance if switching brands. 1, 4
The dose-dependent gastrointestinal side effects (bloating, flatulence in ~20% of patients) are more clinically relevant than glucose concerns. 5, 6