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Xenical Side Effects

Generic name: orlistat

Medically reviewed by Last updated on Feb 14, 2024.

Note: This document contains side effect information about orlistat. Some dosage forms listed on this page may not apply to the brand name Xenical.

Applies to orlistat: oral capsule.

Serious side effects of Xenical

Along with its needed effects, orlistat (the active ingredient contained in Xenical) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking orlistat:

More common

Less common


Incidence not known

Other side effects of Xenical

Some side effects of orlistat may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

Less common

For Healthcare Professionals

Applies to orlistat: oral capsule.


The most commonly reported adverse events have included oily spotting, flatus with discharge, fecal urgency fatty/oily stool, oily evacuation, increased defecation and fecal incontinence.[Ref]


Gastrointestinal events usually occur within the first 3 months. Approximately 50% of all GI events lasted for less than 1 week with a majority lasting no more than 4 weeks. Although, in some individuals, gastrointestinal events have lasted 6 months or more. In clinical trials, gastrointestinal adverse effects were the most common reason for treatment discontinuation.[Ref]

Very common (10% or more): Oily spotting (up to 26.6%), flatus with discharge (up to 23.9%), fecal urgency (up to 22.1%), fatty/oily stool (up to 20%), oily evacuation (up to 11.9%), increased defecation (up to 10.8%), abdominal pain/discomfort (up to 25.5%)

Common (1% to 10%): Fecal incontinence, nausea, infectious diarrhea, rectal pain/discomfort, tooth disorder, gingival disorder, vomiting

Frequency not reported: Abdominal distention

Postmarketing reports: Pancreatitis, lower gastrointestinal bleeding[Ref]


Postmarketing reports: Increases in hepatic transaminases, alkaline phosphatase elevations, hepatitis, hepatic failure, liver transplant[Ref]

Reports of hepatic failure have been received during postmarketing surveillance, with some of these cases resulting in liver transplant or death. Rare cases of increased transaminases, alkaline phosphatase, and hepatitis have been received.[Ref]


Postmarketing reports: Hypersensitivity reactions including pruritus, rash, urticaria, angioedema, bronchospasm, and anaphylaxis; at least one case of cutaneous leukocytoclastic vasculitis[Ref]


Frequency not reported: Hypoglycemia, at least one case of diabetic ketoacidosis; polyuria, polydipsia[Ref]


Cases of leukocytoclastic vasculitis have been reported during the postmarketing period. Clinical signs include palpable purpura, maculopapular lesions, or bullous eruption.[Ref]

Postmarketing reports: Bullous eruption, leukocytoclastic vasculitis[Ref]


Postmarketing reports: Acute oxalate nephropathy[Ref]

Nervous system

Convulsions have been reported in patients concomitantly receiving this drug with antiepileptic drugs.[Ref]

Very common (10% or more): Headache (up to 30.6%)

Common (1% to 10%): Dizziness

Postmarketing reports: Convulsions[Ref]


Common (1% to 10%): Sleep disorder, anxiety, depression[Ref]


Very common (10% or more): Influenza (up to 39.7%), upper respiratory infection (up to 38.1%)

Common (1% to 10%): Lower respiratory infection, ear, nose & throat symptoms[Ref]


Very common (10% or more): Back pain (up to 13.9%)

Common (1% to 10%): Arthritis, myalgia, joint disorder, tendonitis[Ref]


Common (1% to 10%): Menstrual irregularity, vaginitis, urinary tract infection[Ref]


Common (1% to 10%): Pedal edema[Ref]


Postmarketing reports: Decreased prothrombin, increased INR and unbalanced anticoagulant treatment[Ref]

Decreased prothrombin and increased INR resulting in unbalanced anticoagulant treatment has been reported in patients treated concomitantly with anticoagulants.[Ref]


Common (1% to 10%): Fatigue, otitis[Ref]


For patients receiving levothyroxine, hypothyroidism has been reported requiring an adjustment to levothyroxine therapy.[Ref]

Postmarketing reports: Hypothyroidism[Ref]


1. Product Information. Xenical (orlistat). Roche Laboratories. 2001;PROD.

2. Product Information. alli (orlistat). GlaxoSmithKline Healthcare. 2018.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.