Most adults in the world make much less lactase, the enzyme that digests milk sugar, after early childhood. For many of them a glass of milk brings bloating, gas, cramps or loose stools a few hours later. That is lactose intolerance, and the supplement aisle offers lactase pills, drops, probiotics and prebiotics to help.
The good news is that lactose intolerance is usually manageable, and most people do not need to give up dairy. The less obvious news is that dairy is not always the cause of the symptoms blamed on it, and the supplements work better for some people and products than others.
The short version
- Most adults with lactose intolerance can still have some dairy. A review for a US National Institutes of Health conference found that most tolerate 12 to 15 g of lactose, about a cup of milk, and having dairy with a meal may help further.
- Symptoms are not always caused by lactose. In a blinded trial, people who called themselves severely lactose intolerant had minimal symptoms from a cup of regular milk, with no significant difference in symptom severity compared with lactose-free milk.
- Lactase pills help many people, not everyone. Small trials show they reduce lactose reaching the colon and often ease symptoms, but results vary by product, dose and person. Take them with the first bite or sip.
- Yogurt with live cultures and hard cheeses are easier to digest. The live cultures in yogurt help digest its own lactose, an effect European regulators accept.
- Probiotic and prebiotic evidence is thin. A prebiotic drug candidate (RP-G28) missed its main goal in a 557-person phase 3 trial.
- Protect your calcium and vitamin D if you cut back on dairy, and see a doctor if symptoms start later in life or come with weight loss, anemia or blood in the stool.
- Not for milk allergy or galactosemia. Lactase pills and lactose-free milk do not protect against a milk allergy, and lactose-free milk still contains galactose, so it is not safe for people with galactosemia.
What lactose intolerance is
Lactose is the natural sugar in milk. To absorb it, the small intestine uses lactase to split it into two simpler sugars, glucose and galactose. Lactose that is not split travels to the colon, where gut bacteria ferment it into gas and draw in fluid. That causes the symptoms.
There are three main reasons for low lactase:
- Lactase non-persistence (the common, genetic kind). In most people, lactase production falls after early childhood. Reviews estimate that roughly 65 to 70 percent of the world's adults are affected, with large differences by ancestry: it is less common in people of northern European descent and some African, Middle Eastern and South Asian groups. Symptoms may not start until later childhood, the teen years or early adulthood.
- Secondary lactase deficiency. Damage to the small intestine from a gut infection, celiac disease, Crohn's disease, surgery, some medicines or radiation can lower lactase. It may improve once the cause is treated.
- Congenital lactase deficiency. A rare condition in which a baby makes little or no lactase from birth.
Two terms are worth separating. Lactose malabsorption means some lactose is not digested; lactose intolerance means it causes symptoms. Many people with malabsorption have no symptoms at normal intakes. And lactose intolerance is not a milk allergy: a cow's milk allergy is an immune reaction to milk proteins, which can be dangerous, and lactase pills or lactose-free milk do nothing for it.
Lactose intolerance symptoms and how much dairy you can handle
Typical symptoms are bloating, gas, abdominal pain or cramps, diarrhea, nausea and a rumbling stomach, usually starting within a few hours of eating dairy and sometimes within minutes. How bad they are depends on how much lactose you have, what you eat it with, and your gut bacteria.
Most people do not need a lactose-free diet. A systematic review of 36 randomized trials, prepared for a 2010 NIH consensus conference, found moderate-quality evidence that 12 to 15 g of lactose, about a cup of milk, is well tolerated by most adults with presumed lactose intolerance. The panel concluded that most people do not need to eliminate dairy completely.
Dose and context matter. In a small trial that gave lactose in water on an empty stomach, pain increased at 12 g and gas at 20 g, and the authors suggested foods with 6 g or less per serving, such as hard cheeses and small servings of milk. Spreading dairy through the day and having it with meals tends to help.
| Option | Why it helps | Good to know |
|---|---|---|
| Smaller servings with meals | Less lactose at once, slower digestion | About a cup of milk is tolerated by most adults |
| Hard aged cheeses (cheddar, Swiss) | Little lactose left after aging | Often fine even for sensitive people |
| Yogurt with live cultures | Its bacteria help digest its own lactose | Look for "live and active cultures" |
| Lactose-free milk | Lactose already split by added lactase | Same calcium as regular milk; tastes a little sweeter; not for milk allergy or galactosemia |
| Lactase pills or drops | Add the missing enzyme | Results vary; take with the first bite or sip |
Is it really lactose?
Several blinded trials suggest that many people blame lactose for symptoms it does not cause:
- A cup of milk caused little trouble. In a 1995 trial in the New England Journal of Medicine, 30 people who described themselves as severely lactose intolerant drank a cup of regular or lactose-free milk daily for a week each, without knowing which. Symptoms were minimal with both, and 9 of the 30 actually digested lactose normally.
- Lactose-free milk caused symptoms too. In a 1996 trial, 64 percent of people with lactose malabsorption had symptoms after lactose-free milk, the same share as after milk with 7 g of lactose.
- Expectation matters. In a 2010 study, people who had symptoms despite a negative lactose breath test took a sham test with almost no sugar (1 g of glucose), and 44 percent still reported symptoms. So did about a quarter (26 percent) of people with confirmed lactose intolerance. The authors concluded that a nocebo effect, real symptoms set off by expecting them, was likely involved.
Lactose intolerance is real, but gut symptoms after dairy can also come from irritable bowel syndrome (IBS), other poorly absorbed carbohydrates called FODMAPs (which gut bacteria ferment, found in foods such as onions, wheat, beans and some fruits) or anxiety about food. In a 2019 analysis, people with IBS were more likely to report lactose intolerance, but not more likely to have lactose malabsorption. If cutting dairy does not clearly help, lactose may not be your main trigger. None of this means the symptoms are imagined; they are real, and finding the actual cause is the best route to relief.
Lactose intolerance tests: how it is diagnosed
- Hydrogen breath test. You drink a set dose of lactose (usually 25 g) and breathe into a device every 30 minutes or so for a few hours. A rise of at least 20 parts per million in breath hydrogen means lactose reached the colon. European guidance says a positive breath test should be paired with a symptom check, because malabsorption without symptoms is not intolerance. Some people produce methane instead of hydrogen, and bacterial overgrowth in the small intestine (SIBO) can cause false positives.
- Genetic test (LCT -13910). It shows whether you carry the common European lactase-persistence variant. It matched breath tests well in German patients, but it says nothing about symptoms, misses secondary causes and is less reliable in people of African or Asian ancestry.
- Elimination and challenge. Cutting dairy for a couple of weeks and then bringing it back is simple, but open to the expectation effects above. A fairer home version is to have someone else serve you regular or lactose-free milk without telling you which.
Home "food sensitivity" kits that measure IgG antibodies do not diagnose lactose intolerance; see our guide to at-home gut and food sensitivity tests.
- Symptoms start for the first time in adulthood, keep coming back, or appear in a young child: lactose problems in children under about 5 are usually caused by another gut condition.
- You have weight loss without trying, anemia, blood in the stool or black stools, or a family history of celiac disease, inflammatory bowel disease or colon cancer.
Do lactase supplements work? What the trials show
Lactase supplements are made from fungal or yeast enzymes (from Aspergillus or Kluyveromyces) and come as chewable tablets, caplets and liquid drops. The trials are small, mostly use lactose challenges in a lab, and test products that have changed since:
- They usually reduce undigested lactose. In 1990s trials, chewable tablets taken with 50 g of lactose lowered breath hydrogen and eased cramping and gas in 24 adults, and three brands taken with milk containing 20 g of lactose all sharply reduced breath hydrogen, with a double dose (about 6,000 units) working better than a single one.
- Symptom relief is less consistent. In a 10-person trial with ice cream, three products gave different results: the one that lowered breath hydrogen did not ease symptoms, and the other two eased some symptoms without lowering it. With a very large load (50 g of lactose in water), the enzymes appeared to be overwhelmed and did not significantly reduce breath hydrogen or symptoms.
- Not everyone responds. In a 2014 study of 96 people with lactose malabsorption and no placebo group, a single 15,000-unit dose of tilactase, taken an hour before the test, normalized the breath test in about 22 percent, improved it in about 18 percent and left 60 percent essentially unchanged.
- Pre-treating milk works well. In a 30-person crossover trial, adding a yeast lactase (from Kluyveromyces lactis) to milk 10 hours before drinking it gave the lowest symptom scores, better than adding twice the dose just before. That is essentially homemade lactose-free milk.
The review prepared for the NIH conference could not pool the trials because they differed so much, and it judged the evidence for lactose-intolerance treatments insufficient. Even so, the European Union authorizes the claim, based on a European Food Safety Authority opinion, that lactase improves lactose digestion in people who have difficulty digesting it, for food supplements providing at least 4,500 FCC units taken with each meal containing lactose. FCC (Food Chemicals Codex) units are a standard lab measure of enzyme strength; a higher number means a stronger dose.
Practical tips: take lactase with the first bite or sip of a dairy food; for a long meal or a large serving, labels often suggest another dose; compare products by FCC units; and know that lactose-free milk does the job reliably because the lactose is split before you drink it. Our digestive enzyme ranking includes a lactase pick.
Lactase does nothing for a milk allergy or for galactosemia, and lactose-free milk is not safe for people with galactosemia (see Who should be careful).
Yogurt, probiotics and prebiotics
Yogurt with live cultures. This has the strongest food evidence. In a 1984 study, 18 g of lactose in yogurt produced only about a third as much breath hydrogen as a similar amount in milk or water, with fewer reports of diarrhea or gas, apparently because the yogurt bacteria release their own lactase in the gut. European regulators accept that live cultures (Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, at least 100 million live bacteria per gram) improve digestion of the lactose in that yogurt or fermented milk. The claim covers the yogurt itself, not capsules or other foods.
Probiotic supplements. Reviews describe the evidence as scarce and of limited quality. A 2022 review of probiotics and prebiotics found only 5 eligible randomized trials, and just 3 of them tested probiotics: one strain (B. bifidum 900791) did not help, while L. reuteri DSM 17938 and L. acidophilus DDS-1 improved some symptoms in small trials. In one 60-person trial, L. reuteri helped, but less than lactase. A strain of B. lactis (Bi-07) lowered breath hydrogen in two trials published by researchers at its maker, but the European Food Safety Authority found no cause-and-effect benefit because symptoms did not improve. Our probiotic ranking covers general options, and our probiotics vs prebiotics guide explains the difference.
Prebiotics (GOS) and "training" your gut. Galacto-oligosaccharides (GOS) are short chains of sugars made from lactose. As a prebiotic, they feed gut bacteria, including the ones that digest lactose. A highly purified GOS drug candidate, RP-G28, looked promising in a 377-person trial (40 versus 26 percent responders), but in its 557-person phase 3 trial in 2019 it missed its main goal, and it has not been approved. Its results do not transfer to ordinary GOS supplements. Eating gradually more lactose over 10 days lowered breath hydrogen and gas in a 20-person trial, but in a 46-person trial symptoms improved just as much with ordinary sugar (sucrose), so part of the symptom benefit may be expectation. Neither probiotics nor prebiotics switch your lactase gene back on.
Calcium and vitamin D
The NIH panel warned that people who avoid dairy because of real or perceived intolerance often get too little calcium and vitamin D, which may harm bone health. A 2019 review concluded that neither lactose nor lactase deficiency significantly affects calcium absorption in adults; the risk comes from cutting out dairy without replacing it.
- Lactose-free milk and yogurt keep the same calcium as regular dairy.
- Other calcium sources include canned salmon or sardines with soft bones, tofu made with calcium, broccoli and leafy greens, almonds, beans and fortified foods.
- Plant milks vary. FDA consumer guidance (updated March 2026) says US dietary guidance includes only fortified soy drinks in the dairy group; check labels for calcium, vitamin D and protein.
Adults need 1,000 mg of calcium a day (1,200 mg for women over 50 and adults over 70). If food falls short, a calcium supplement and vitamin D can fill the gap; see our calcium and vitamin D deficiency guides. Stay under the upper limit of 2,500 mg of calcium a day (2,000 mg over age 50) from food and supplements combined. Our calcium carbonate vs citrate guide helps with choosing a form.
Who should be careful
Lactase supplements were well tolerated in trials. Most people with lactose intolerance also do not need to avoid medicines that contain a small amount of lactose as a filler: in a trial of 77 people with lactose intolerance, a 400 mg dose of lactose, the amount suggested as a ceiling for a tablet or capsule, caused no more symptoms or breath hydrogen than placebo, so the finding applies to medicines with 400 mg of lactose or less. If even small amounts bother you, ask your pharmacist about lactose-free versions; do not stop a prescribed medicine on your own.
- Galactosemia. Lactase does not help, and lactose-free milk is not safe, because splitting lactose releases galactose. People with galactosemia follow a lifelong diet that removes lactose and galactose from milk and dairy foods, under the care of a metabolic specialist.
- Milk allergy. Lactase and lactose-free milk still contain milk proteins and do not protect against an allergic reaction.
- Babies and children. Do not remove dairy from a child's diet without medical advice. A 2024 review found the evidence for lactase drops in infant colic inconclusive.
- Labels. Chewable and flavored products can contain sweeteners or sugar alcohols, which matter if you follow a low-FODMAP diet.
Frequently asked questions
What are the symptoms of lactose intolerance, and how soon do they start?
Bloating, gas, abdominal pain or cramps, diarrhea, nausea and a rumbling stomach, usually starting within a few hours of eating or drinking dairy and sometimes within minutes. How strong they are depends on how much lactose you have and what you eat it with. See a doctor if symptoms are new in adulthood or come with weight loss, anemia or blood in the stool.
Can lactose intolerance develop later in life?
Yes. In the common genetic type, lactase falls after early childhood, and symptoms may not start until later childhood, the teen years or early adulthood. Lactose trouble can also start later in adulthood after a gut infection, celiac disease, Crohn's disease, surgery or some medicines, so new symptoms in an adult are worth checking with a doctor.
How much dairy can you have if you are lactose intolerant?
Most adults with lactose intolerance tolerate 12 to 15 g of lactose, about a cup of milk, according to a review prepared for a US National Institutes of Health conference. Having dairy with meals, spreading it through the day, and choosing yogurt with live cultures or hard aged cheeses usually helps.
Do lactase pills work?
For many people, yes, but not for everyone. Small trials show lactase taken with dairy reduces the lactose that reaches the colon and often eases symptoms, but results vary by product, dose and person, and very large amounts of lactose can overwhelm a dose. Take it with the first bite or sip. Lactose-free milk, which has the lactose already split, is a reliable alternative. Neither protects against a milk allergy, and lactose-free milk is not safe for people with galactosemia.
What should you look for in a lactase supplement?
Check the strength in FCC units per dose. The European Union authorizes a lactose-digestion claim for supplements providing at least 4,500 FCC units taken with each meal that contains lactose. In one trial, chewable, caplet and soft-gel forms worked about equally at the same dose, and in another, lactase added to milk hours ahead of drinking it worked best. Chewable and flavored products may contain sugar alcohols, which matter if you follow a low-FODMAP diet.
Is lactose-free milk healthy?
For most people, yes. It is regular milk with lactase added, so it keeps the same protein, calcium and other nutrients. It tastes a little sweeter because the lactose has been split into glucose and galactose. It still contains milk protein and galactose, so it is not suitable for anyone with a milk allergy or galactosemia.
How is lactose intolerance diagnosed?
Usually with a hydrogen breath test: you drink a set amount of lactose and your breath is measured over a few hours. A genetic test shows whether you carry the common European lactase-persistence variant, but it says nothing about symptoms and is less reliable for people of African or Asian ancestry. A simple elimination and reintroduction, ideally without knowing which milk you are drinking, can also help.
Do probiotics help lactose intolerance?
The evidence is thin. A 2022 review of probiotics and prebiotics found only five eligible randomized trials, three of them on probiotics: two strains improved some symptoms in small studies, while a third did not help. Yogurt with live cultures has better evidence, because its bacteria help digest the lactose in that yogurt.
Is lactose intolerance the same as a milk allergy?
No. Lactose intolerance is trouble digesting milk sugar. A milk allergy is an immune reaction to milk proteins and can be serious. Lactase pills and lactose-free milk do not protect against a milk allergy.
Do you need a calcium supplement if you avoid dairy?
Possibly. People who avoid dairy often get too little calcium and vitamin D. Lactose-free dairy has the same calcium as regular dairy, and canned fish with bones, calcium-set tofu, leafy greens and fortified foods also help. If your diet still falls short of 1,000 to 1,200 mg of calcium a day, a supplement can fill the gap.
The bottom line
Lactose intolerance is common and usually manageable without giving up dairy. Most adults handle about a cup of milk, especially with food, and yogurt with live cultures, hard cheeses and lactose-free milk widen the options. Blinded trials show that some symptoms blamed on lactose have other causes, so a fair test is worth doing before cutting dairy out.
Lactase supplements reduce undigested lactose for many people and are a reasonable tool, though results vary by product and person. Probiotic and prebiotic evidence is thin, and the most promising prebiotic failed its main trial. If you do cut back on dairy, make up the calcium and vitamin D, and see a doctor if symptoms start later in life or come with weight loss, anemia or blood in the stool.