Lactase pills have a simple job, and when they seem to fail, the reason is usually simple too. The dose was too small for the meal. The pill came too late. Or lactose wasn't the real problem.
This guide covers how lactase supplements work, what the studies show and how to use them for the best chance of success.
How lactase works, and what the research shows
Lactase is the enzyme that splits lactose, the natural sugar in milk, into two smaller sugars your small intestine can absorb. If you make less lactase, undigested lactose travels on to the colon, where bacteria ferment it. Supplements supply lactase made by microbes, such as yeasts, to do that job in your gut or in the milk itself.
- In a double-blind crossover study, 24 people with lactose intolerance drank milk containing 50 grams of lactose, a very large amount. With 3 chewable lactase tablets (9,900 FCC units in total), their breath hydrogen peaked lower than with placebo, and cramping, belching, gas and diarrhea were rated less severe in the first eight hours (Sanders et al., 1992).
- In a placebo-controlled crossover trial of 47 people with lactose intolerance confirmed by a breath test, chewable lactase tablets improved symptom scores and cut total breath hydrogen by 55% (Baijal and Tandon, 2021).
- A study comparing three lactase products found that with milk containing 20 grams of lactose, all of them reduced breath hydrogen and symptoms, and about 6,000 units worked better than about 3,000. With 50 grams of lactose in water, though, neither dose made a significant difference to symptoms (Lin et al., 1993).
The takeaway: lactase supplements generally help, but a standard dose has limits, and a very large lactose load can overwhelm it.
Before you eat
Step 1: Make sure lactose is a likely culprit. Lactose symptoms usually include bloating, gas, cramping or loose stools within hours of eating dairy. If you react the same way to meals with no dairy at all, lactose probably isn't the main issue. A doctor can order a hydrogen breath test if you want a clearer answer.
Step 2: Estimate the lactose in your meal. The more lactose, the more enzyme you'll need. A glass of milk, a milkshake or a bowl of ice cream is an obvious source. But lactose also hides in foods you might not expect, including baked goods, breakfast cereals, drinks and processed meats (Facioni et al., 2020). Scan ingredient lists for milk, milk solids, whey or lactose.
At the meal
Step 3: Take it with the first bite. Lactase has to be in your gut at the same time as the lactose. Take it with your first bites or sips of dairy, as product labels typically direct. If a meal stretches out, like a long dinner with dessert an hour later, check whether your product's label suggests an additional dose.
Step 4: Match the dose to the meal. Lactase strength is listed in FCC units, from the Food Chemicals Codex. The amount that covers a latte may not cover pizza followed by ice cream. Stay within the label directions, and use the higher end of the range for bigger dairy servings, since studies show a dose-response effect (Lin et al., 1993).
Step 5: Consider treating milk ahead of time. Lactase can also be added directly to milk. In a double-blind study of 30 adults aged 18 to 65 (average age 43), adding lactase to milk either 10 hours or 5 minutes before drinking it sharply reduced breath hydrogen and symptoms compared with placebo. Symptom scores were lowest when the milk had been treated 10 hours ahead (Montalto et al., 2005).
If you drink milk daily, treating it the night before is a convenient option. Store-bought lactose-free milk works on the same principle, with lactase added during processing.
