Short answer: In the label's first-year trials, the most common Xenical side effects were bowel changes from fat that is not absorbed: oily spotting (26.6% vs 1.3% on placebo), gas with discharge (23.9% vs 1.4%), urgent bowel movements (22.1% vs 6.7%), fatty or oily stool (20.0% vs 2.9%) and fecal incontinence (7.7% vs 0.9%). These usually started within 3 months. Xenical has no boxed warning.
What Xenical is approved for: Xenical is approved for obesity management, including weight loss and weight maintenance, with a reduced-calorie diet, and to reduce the risk of weight regain after earlier weight loss, in people with a starting BMI of 30 kg/m2 or more, or 27 kg/m2 or more with other risk factors such as high blood pressure, diabetes or high blood fats (section 1). Use in adolescents 12 to 16 is supported by studies (section 8.4).
Source
XENICAL (orlistat) capsules, prescribing information and Patient Information. H2-Pharma (licensed by CHEPLAPHARM). DailyMed, version published January 12, 2026. DailyMed setid 6240792b-9224-2d10-e053-2a91aa0a2c3e
No. The current Xenical label has no boxed warning.
These are the label's own numbers from the Adverse Reactions section. Where the label compares with placebo (a dummy treatment), both columns are shown, so you can see how much more often a reaction happened on Xenical.
| Adverse event | Year 1 Xenical % (N=1913) | Year 1 Placebo % (N=1466) | Year 2 Xenical % (N=613) | Year 2 Placebo % (N=524) |
|---|---|---|---|---|
| Oily Spotting | 26.6 | 1.3 | 4.4 | 0.2 |
| Flatus with Discharge | 23.9 | 1.4 | 2.1 | 0.2 |
| Fecal Urgency | 22.1 | 6.7 | 2.8 | 1.7 |
| Fatty/Oily Stool | 20.0 | 2.9 | 5.5 | 0.6 |
| Oily Evacuation | 11.9 | 0.8 | 2.3 | 0.2 |
| Increased Defecation | 10.8 | 4.1 | 2.6 | 0.8 |
| Fecal Incontinence | 7.7 | 0.9 | 1.8 | 0.2 |
Seven double-blind placebo-controlled trials of Xenical 120 mg three times a day plus diet. Commonly observed means 5% or more and at least twice placebo. Oily discharge may be clear or orange or brown. About half of these episodes lasted under 1 week and most no more than 4 weeks, though some people had them for 6 months or longer.
| Adverse event | Year 1 Xenical % (N=1913) | Year 1 Placebo % (N=1466) | Year 2 Xenical % (N=613) | Year 2 Placebo % (N=524) |
|---|---|---|---|---|
| Abdominal Pain/Discomfort | 25.5 | 21.4 | – | – |
| Nausea | 8.1 | 7.3 | 3.6 | 2.7 |
| Infectious Diarrhea | 5.3 | 4.4 | – | – |
| Rectal Pain/Discomfort | 5.2 | 4.0 | 3.3 | 1.9 |
| Tooth Disorder | 4.3 | 3.1 | 2.9 | 2.3 |
| Gingival Disorder | 4.1 | 2.9 | 2.0 | 1.5 |
| Vomiting | 3.8 | 3.5 | – | – |
| Influenza | 39.7 | 36.2 | – | – |
| Upper Respiratory Infection | 38.1 | 32.8 | 26.1 | 25.8 |
| Lower Respiratory Infection | 7.8 | 6.6 | – | – |
| Ear, Nose & Throat Symptoms | 2.0 | 1.6 | – | – |
| Back Pain | 13.9 | 12.1 | – | – |
| Pain Lower Extremities | – | – | 10.8 | 10.3 |
| Arthritis | 5.4 | 4.8 | – | – |
| Myalgia | 4.2 | 3.3 | – | – |
| Joint Disorder | 2.3 | 2.2 | – | – |
| Tendonitis | – | – | 2.0 | 1.9 |
| Headache | 30.6 | 27.6 | – | – |
| Dizziness | 5.2 | 5.0 | – | – |
| Fatigue | 7.2 | 6.4 | 3.1 | 1.7 |
| Sleep Disorder | 3.9 | 3.3 | – | – |
| Rash | 4.3 | 4.0 | – | – |
| Dry Skin | 2.1 | 1.4 | – | – |
| Menstrual Irregularity | 9.8 | 7.5 | – | – |
| Vaginitis | 3.8 | 3.6 | 2.6 | 1.9 |
| Urinary Tract Infection | 7.5 | 7.3 | 5.9 | 4.8 |
| Psychiatric Anxiety | 4.7 | 2.9 | 2.8 | 2.1 |
| Depression | – | – | 3.4 | 2.5 |
| Otitis | 4.3 | 3.4 | 2.9 | 2.5 |
| Pedal Edema | – | – | 2.8 | 1.9 |
Events at 2% or more on Xenical 120 mg three times a day and more than placebo in year 1 or year 2, regardless of cause. A dash means none reported at 2% or more and above placebo that year. The label's body-system heading rows are left out.
| Vitamin | Placebo | Xenical |
|---|---|---|
| Vitamin A | 1.0% | 2.2% |
| Vitamin D | 6.6% | 12.0% |
| Vitamin E | 1.0% | 5.8% |
| Beta-carotene | 1.7% | 6.1% |
Adults who were not taking vitamin supplements and had normal levels at the start.
In controlled trials, 8.8% of people on Xenical stopped because of side effects vs 5.0% on placebo; the most common reasons were stomach and bowel effects.
Most bowel side effects first appeared within 3 months of starting. In the 4-year XENDOS study, the total rate of bowel-related side effects fell each year.
In adolescents 12 to 16 who all took vitamin supplements (Table 5), low vitamin D on two or more visits was 1.4% on Xenical vs 0.7% on placebo, and low beta-carotene 1.5% vs 0.8%; none had low vitamin A or E.
In a trial for preventing type 2 diabetes, gallstones were reported in 2.9% (47/1649) on Xenical vs 1.8% (30/1655) on placebo.
In trials in people with obesity and diabetes, low blood sugar and abdominal bloating were also seen.
Reported after approval: rare serious liver problems including liver failure, rare allergic reactions (itching, rash, hives, angioedema, bronchospasm, anaphylaxis), rare vasculitis, acute oxalate kidney damage, pancreatitis and lower GI bleeding, mostly not serious.
The Warnings and Precautions part of the label lists these. Each line gives the label's heading and what it means in plain words.
Who should not use it. People who are pregnant, have chronic malabsorption syndrome or cholestasis (a bile-flow problem), or have a known allergy to Xenical or its ingredients.
Drug interactions and lower vitamin absorption. Xenical can lower absorption of some fat-soluble vitamins and beta-carotene, so a daily multivitamin with vitamins A, D, E, K and beta-carotene is advised, taken at least 2 hours apart from Xenical. It also interacts with cyclosporine, levothyroxine, warfarin, amiodarone, seizure medicines and HIV medicines. Weight loss may change blood sugar control, and diabetes medicine doses may need lowering.
Liver injury. Rare reports of severe liver injury, including acute liver failure, have been received, some leading to liver transplant or death. Signs include loss of appetite, itching, yellow skin or eyes, dark urine, light stools or pain in the upper right abdomen. If these occur, Xenical and other suspect medicines are stopped and liver tests are done.
Oxalate kidney stones and kidney damage. Urine oxalate can rise, and oxalate kidney stones and oxalate kidney damage with kidney failure have been reported. Kidney function is monitored in people at higher risk, such as those with kidney impairment or past calcium oxalate stones, and Xenical is stopped if oxalate kidney damage develops.
Gallstones. Substantial weight loss can raise the risk of gallstones (2.9% vs 1.8% on placebo in one trial).
Diet and other causes of obesity. Medical causes of obesity, such as an underactive thyroid, are ruled out first. Bowel side effects may increase with a diet above 30% of calories from fat or with any one very high-fat meal.
Misuse. As with any weight-loss medicine, Xenical could be misused by people with eating disorders such as anorexia nervosa or bulimia.
From the Patient Information that comes with Xenical:
Dose Track has a side-effect log. Each entry records the symptom, a severity (none, mild, moderate, severe or life-threatening), the date and an optional note, and can be tied to a specific dose or logged on its own. The history screen shows what you logged over time, which makes it easier to tell your prescriber when a reaction started and whether it is easing. The app records what you enter; it does not judge whether a symptom is serious. For anything on the label's call-your-doctor list, call your doctor.
This page is what the FDA label says, in plain words. It is not medical advice. Follow your prescriber, and ask them or your pharmacist about anything here.