Alli Weight Loss: Does It Work?

Craig Primack, MD, FACP, FAAP, FOMA

Reviewed by Craig Primack, MD, FACP, FAAP, FOMA

Written by Hadley Mendelsohn

Published 04/24/2024

Updated 04/26/2024

Alli® (orlistat), an over-the-counter (OTC) weight loss medication can help people lose a modest amount of weight when used exactly (we’ll say it again for emphasis: exactly) as directed. When taking Alli, you’ll need to follow a strictly low-calorie, low-fat diet if you want to reduce your risk of some pretty unpleasant side effects.

Alli definitely isn’t right for everyone. If you’ve already done a deep dive into the ~bowels~ of the internet to uncover Alli horror stories, you may be here for a bit of emotional support. Keep reading to learn more about Alli, its side effects, and how much weight you can expect to lose. We’ll also cover alternatives to Alli so that you can make the choice that’s right for you.

Alli is the only FDA-approved weight-loss medication available over the counter. This means you can pick it up at any local pharmacy or online retailer without a prescription.

Alli is designed to promote weight loss in adults with a body mass index (BMI) of 25 or higher, when used alongside a reduced-calorie, low-fat diet.

Adults take one of these weight loss pills with each meal (but no more than three per day).

Alli belongs to a class of drugs known as lipase inhibitors. They work by reducing the amount of fat you absorb from your diet, allowing it to pass quickly through your body. Which means that instead of absorbing all the fat you eat, you’ll poop it out.

Orlistat, the active ingredient in Alli, is also available as a prescription (sometimes sold under the brand name Xenical). It’s typically prescribed to folks who have overweight or obesity along with conditions like high blood pressure, diabetes, or heart disease.

Your doctor might also prescribe it if you’ve lost a significant amount of weight and worry about the possibility of gaining it back.

Prescription orlistat is available as a 120 mg tablet — roughly the same as taking two 60 mg pills of Alli per day.

Studies show that people taking orlistat lose about 6 pounds more than people who don’t take orlistat. But keep in mind that these studies are generally done under controlled settings, where healthcare professionals are monitoring you and your diet.

In the real world, things can be different.

Still, research shows that orlistat increases the likelihood that you’ll lose 5 to 10 pounds over the course of six months.

On top of being a weight loss aid, another study found that Alli can lower LDL-cholesterol levels by about 10 percent. Sometimes called the “bad cholesterol,” reduced LDL levels can improve your overall health.

Alli also appears to encourage healthier lifestyle habits, like eating a lower-fat diet. Of course, this could be because of what can happen when you cheat!

Prescribed online

Weight loss treatment that puts you first

Let’s get straight to it. Back when Alli first debuted, there were a lot of jokes about the notorious Alli “oops factor.”

While by no means a guarantee, these unpleasant gastrointestinal side effects do affect a lot of people. It makes sense that the most common side effect is a change in bowel habits — Alli works by helping you pass dietary fat when you go to the bathroom.

Side effects often lead people to stop taking the medication before they’ve seen much weight loss.

According to one study, the most common side effect is known as fatty stool. An excess of fat in stool makes it looser, smellier, and paler.

A lot of people taking Alli also experience gas with oily spotting (which a lot of people report ruins their underwear and clothing), loose stools, and more frequent, difficult-to-control and extremely urgent bowel movements. Sticking to a low-fat diet will decrease the likelihood of experiencing these side effects.

The good news is that these side effects usually just happen during the first couple of weeks of treatment. Although depending on eating habits, they can persist.

More serious, but less common Alli side effects include:

  • Abdominal pain and discomfort

  • Loss of appetite

  • Anxiety

  • Pain in the rectum

  • Headache

  • Nausea and vomiting

  • Dark urine

  • Irregular menstrual periods

  • Hives, rashes and itching

  • Excessive tiredness or weakness

  • Liver damage

Managing Alli Side Effects

Basically, you’re not going to want to take Alli if you’re planning on eating a high-fat meal. Skipping your dose before a particular meal might help a little, but it’ll still be a gamble.

You can limit your risk of gastrointestinal side effects by keeping your fat intake low. If you’re committed to a low-fat, low-calorie diet, Alli could be right for you and your weight loss goals.

One other thing worth calling out: Alli may reduce your ability to absorb certain vitamins from your diet. So you should consider taking a multivitamin once a day, preferably at bedtime.

Who Shouldn’t Take Alli?

Even though Alli is available over the counter, you should definitely consult a doctor before taking it. If you are living with an eating disorder or you’ve experienced disordered eating in the past, consider speaking with a mental health professional before exploring Alli.

If you are pregnant or breastfeeding, Alli might not be right for you. Talk with a doctor about any potential risks. Talk with a doctor if you take any take any of the following medications:

  •   Blood pressure medications

  • Other weight loss pills or injections

  • Thyroid medications

  • Blood thinners (like warfarin)

  • Weight loss supplements

Or if you live with any of the following conditions.

  • Pancreatitis

  • Kidney stones

  • Diabetes

  • Thyroid disease

  • Liver transplant

If it sounds like Alli isn’t the right fit for you, there are other weight loss medications you can look into. If you’re living with overweight or obesity, some of these other medications can help you lose more weight than you would with Alli. And you won’t have to worry as much about the “oops.”

Other medications that can help you lose weight, if you need to, include weight loss injections and oral meds like:

  • Semaglutide (Ozempic® and Wegovy®)

  • Liraglutide (Saxenda® and Victoza®)

  • Tirzepatide (Mounjaro® and Zepbound®)

  • Metformin

  • Topamax® (topiramate)

  • Qsymia® (phentermine-topiramate)

  • Contrave® (naltrexone-bupropion)

Other strategies to help you meet your weight loss goals include:

  • Establishing a solid workout routine and getting plenty of steps

  • Eating a healthy diet

  • Improving your sleep hygiene (make sure you aim for seven to nine hours a night!)

  • Staying hydrated

  • Reducing stress

Whether you opt for Alli or not, taking an online assessment (for free!) can be a good place to find out the right holistic weight loss routine for you.

7 Sources

  1. “Body Mass Index Table 1,” n.d. Retrieved from:
  2. “DailyMed - ALLI- Orlistat Capsule.” n.d. Retrieved from:
  3. Williams, G. (2007). Orlistat over the counter. BMJ : British Medical Journal, 335(7631), 1163-1164. Retreived from:
  4. “Orlistat: MedlinePlus Drug Information.” 2016. January 15, 2016. Retrieved from:
  5. Glaxo Smith Kline Consumer Healthcare, “Alli Companion Guide: How to make the alli® Program your partner for successful weight loss.” 2013. Retrieved from:
  6. National Institute of Child Health and Human Development. “Orlistat.” Drugs and Lactation Database (LactMed®) - NCBI Bookshelf, April 19, 2021. Retrieved from:
  7. Rucker D, et al. (2007) Long term pharmacotherapy for obesity and overweight: updated meta-analysis.
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