Lactase is an enzyme that breaks lactose down into galactose and glucose. A lack of ability to produce enough lactase is the major reason why people are lactose intolerant. Secondary intolerance can be due to gut health issues. Lactase is frequently added to milk or taken during meals to aid in digesting lactose.
Can simply taking lactase as a supplement allow people to digest lactose more effectively? That appears to be the case, as supplementation of lactose proved effective in many human trials, with reductions in breath hydrogen (a sign of fermentation) and various symptoms such as flatulence, bloating, abdominal pain, and diarrhea—the most common symptoms of lactose intolerance.
Simply taking lactase may not necessarily eliminate symptoms, and many of the studies still found that those with lactose interolance still experienced more fermentation when taking lactase than those who weren't lactose intolerant, and had worse symptoms. There's some evidence to suggest that higher doses and milk pretreatment for 24 hours or more are good solutions, and it's probably best to err on the side of a higher dose.
We haven't evaluated that yet, but it's not foreign to the body, so the risk is probably low.
Rules of thumb used to calculate the amount of lactase are 7500 units for 16 grams of lactose (roughly one normal glass of milk), and 3000 units for 5 g, which is similar but higher.
Of these, the latter was more likely to lead to a meantingful reduction when taken orally. This makes sense given the dynamic nature of the digestive tract, so doses of lactase shouldn't be based on the amount needed to hydrolyze lactase, but on in vivo evidence. Other studies generally suggest that less than 3000 units per 5 g leads to less impressive reductions in lactose fermentation.