Orlistat is taken as a capsule with each main meal that contains fat, up to three times per day. It works by blocking your body from absorbing roughly 30% of the fat you eat, and the way you time your doses, structure your meals, and handle supplements all directly affect how well it works and how comfortable you’ll be while taking it.
Prescription vs. Over-the-Counter Doses
Orlistat comes in two strengths. The prescription version (sold as Xenical) is 120 mg per capsule. The over-the-counter version (sold as Alli) is 60 mg per capsule. Both are taken the same way: one capsule with each fat-containing meal, up to three times daily. That means your maximum is three capsules per day, not three at once.
When to Take Each Dose
Take your capsule during the meal or within one hour after finishing it. The medication needs to be present in your digestive system while your body is breaking down the fat from that meal. If you take it hours later, it won’t have much effect.
If you skip a meal or eat something that contains no fat, skip that dose entirely. Orlistat has nothing to act on without dietary fat, so taking it with a fat-free meal is pointless. Just resume your normal dosing at the next fat-containing meal. If you forget a dose during or after a meal, take it within the hour. If more than an hour has passed, skip it and move on.
The 30% Fat Rule
This is the single most important dietary detail for anyone taking orlistat. The FDA recommends that each meal contain no more than about 30% of its calories from fat. Going over this threshold is the primary cause of the unpleasant digestive side effects the drug is known for.
In practical terms, here’s what 30% of calories from fat looks like across different daily calorie targets:
- 1,500 calories per day: about 50 grams of fat total
- 1,600 calories per day: about 53 grams of fat total
- 1,800 calories per day: about 60 grams of fat total
- 2,000 calories per day: about 67 grams of fat total
Spread that fat roughly evenly across your three meals. On a 1,500-calorie diet, that’s around 15 to 17 grams of fat per meal. Reading nutrition labels becomes genuinely useful here. A single fast-food burger can contain 30 or more grams of fat in one sitting, which would blow past your per-meal target and almost certainly trigger side effects.
Managing Digestive Side Effects
Orlistat blocks fat absorption in your gut, which means undigested fat has to go somewhere. The result can include oily or fatty stools, oily spotting on underwear, increased gas, urgent bowel movements, and difficulty controlling them. These effects aren’t a sign that something is going wrong. They’re the direct, mechanical consequence of unabsorbed fat passing through your lower digestive tract.
The intensity of these side effects is almost entirely controlled by how much fat you eat. Stick to the 30% guideline and most people find the effects manageable. Eat a high-fat meal while on orlistat and you’ll likely experience noticeable oily discharge or urgency within hours. Many people who stop taking orlistat cite these effects as the reason, but in most cases the issue is dietary fat intake, not the drug itself. Some people find it helpful to start with lower-fat meals during the first week or two while they adjust.
There is also an increased risk of kidney stones with orlistat use. When unabsorbed fat reaches the lower intestine, it can increase the absorption of a compound called oxalate, which contributes to stone formation. Staying well hydrated and keeping dietary fat within the recommended range both help reduce this risk.
Vitamins and Supplements
Because orlistat blocks fat absorption, it also reduces absorption of vitamins that dissolve in fat: vitamins A, D, E, K, and beta-carotene. You should take a daily multivitamin that contains all of these. The key detail is timing: take your multivitamin at least two hours before or two hours after your orlistat dose so the medication doesn’t interfere with absorption. Many people find it easiest to take their multivitamin at bedtime, well after their last meal and dose.
Medications That Need Special Timing
If you take thyroid medication (levothyroxine), you need to separate it from orlistat by at least four hours. Cases of underactive thyroid have been reported when the two are taken too close together, because orlistat can interfere with how well your body absorbs the thyroid hormone. If you already take levothyroxine first thing in the morning on an empty stomach, your breakfast dose of orlistat later in the morning will typically fall outside that four-hour window, but it’s worth checking your routine.
If you take a blood thinner like warfarin, orlistat can reduce vitamin K absorption enough to shift your clotting levels. This doesn’t mean you can’t take both, but your clotting values will need closer monitoring, especially when you first start orlistat or change your dose.
What to Expect for Weight Loss
Orlistat produces modest but meaningful weight loss when combined with a reduced-calorie diet. In a large clinical trial, people taking orlistat lost an average of 10.2% of their body weight over one year, compared to 6.1% in the group taking a placebo. That extra 4% translates to roughly 4 kilograms (about 9 pounds) of additional weight loss directly attributable to the medication.
The drug also helps with keeping weight off. In the second year of the same trial, people who continued orlistat regained only about half as much weight as those who switched to a placebo. Weight loss with orlistat is gradual. Most people see the biggest changes in the first six months, with results plateauing after that. If you haven’t lost at least 5% of your starting body weight after 12 weeks on the full prescription dose, the medication may not be effective enough to continue.
Quick Reference for Daily Use
- Dose: One capsule (60 mg OTC or 120 mg prescription) with each fat-containing meal
- Maximum: Three capsules per day
- Timing: During the meal or within one hour after
- No-fat meals: Skip the dose
- Fat target: No more than 30% of calories from fat at each meal
- Multivitamin: Daily, at least two hours apart from any orlistat dose
- Thyroid medication: At least four hours apart from orlistat