Orlistat

Limits on what this shows

• Null findings: Hollander 1998 [11], 391 adults with type 2 diabetes, 57 weeks: fat-soluble vitamin levels remained generally normal (reconstructed abstract read through a summarizer). EMA SmPC [2]: vast majority stayed in range. In supplemented pediatric patients, low-vitamin rates stayed at or below 1.5% in all groups [1].
• At-risk subgroups: Unsupplemented users, adolescents (the supplemented adolescent pilot still showed reduced vitamin E absorption [4]), people on very-low-fat intake or with other fat malabsorption.

Regulatory status

Named in the US label: orlistat "has been shown to reduce the absorption of some fat-soluble vitamins and beta-carotene", with a daily multivitamin advised [1]. The EMA SmPC says treatment "may potentially impair the absorption of fat-soluble vitamins (A, D, E and K)" and that most patients treated up to 4 years kept vitamin and beta-carotene levels in the normal range [2].

Population evidence

Label clinical-trial table, unsupplemented adults, years 1 to 2, low vitamin E on 2 or more consecutive visits: 5.8% on orlistat versus 1.0% on placebo; the trial sizes and confidence intervals were not in the text read [1]. McDuffie 2002 [4]: prospective open-label pilot, 17 obese adolescents on orlistat 120 mg three times daily with a daily multivitamin for 3 to 6 months; absorption of alpha-tocopherol fell versus baseline (p<0.001), serum retinol was unchanged. Two independent Tier A sources, both with orlistat in the cohort, both measuring vitamin E (absorption or serum).

Mechanism

Named and plausible: orlistat inhibits gastric and pancreatic lipases and blocks about 30% of dietary fat absorption [1][2]; vitamin E is a fat-soluble vitamin, so less fat absorbed plausibly means less vitamin E absorbed (inference from [1][2]). This is a consequence of the intended effect, not a separate toxicity.

Why not red

The magnitude is small (4.8 percentage points above placebo), serum vitamin E rather than a functional marker was the label endpoint, the adolescent study measured absorption in 17 people, and two Tier A sources report most patients stay in range [2][11]. Red is not met.

Counter-evidence held on record

Counter-evidence and confounding Placebo patients also had subnormal values (1.0%), so some of the signal is background. The label table did not report lipid adjustment in the text read, and serum vitamin E may track blood lipids. Healthy-volunteer vitamin A and E absorption studies were not located or opened. Framing caution This is an absorption-interference finding bounded to unsupplemented users. A daily fat-soluble multivitamin is the label recommendation, taken at least 2 hours before or after orlistat [1]. No supplement dose is recommended here.

Limits on what this shows

• Null findings: Holecki 2005 [6]: 20 obese menopausal women on a 3-month orlistat weight-reduction program (about 11.6 kg lost) with 20 healthy women as a reference group; serum 25(OH)D3, PTH, total calcium and phosphorus "did not change significantly". Obese women had lower vitamin D and higher PTH than controls both before and after, which is baseline status, not a drug effect. Gotfredsen 2001 [7]: 30 obese adults, randomized double-blind, 1 year; bone mineral density fell similarly in both arms and the only variable different between arms was urinary hydroxyproline/creatinine (as summarized); no between-arm vitamin D deficiency outcome was visible in the text read. Hollander 1998 [11]: levels generally normal (summarized).
• At-risk subgroups: Unsupplemented users; adolescents; people with low baseline vitamin D, which is common in obesity and is itself the main confounder.

Regulatory status

Vitamin D is named in the US label vitamin table and the EMA SmPC fat-soluble vitamin warning [1][2].

Population evidence

Label table, unsupplemented adults, years 1 to 2, low vitamin D on 2 or more visits: 12.0% on orlistat versus 6.6% on placebo [1]. McDuffie 2002 [4]: 17 obese adolescents on orlistat with a daily multivitamin; mean vitamin D was lower after 1 month (p<0.02) despite the supplement. Two independent Tier A sources, orlistat in the cohort, vitamin D measured in both.

Mechanism

Named and plausible: vitamin D is a fat-soluble vitamin and orlistat reduces dietary fat absorption by about 30% [1][2] (inference; vitamin D micellar absorption was not separately sourced here).

Why not red

The absolute excess over placebo is 5.4 percentage points, one of the two Tier A sources is a 17-person pilot, and a 3-month adult study with PTH measured found no change [6]. Normal PTH argues against a functional deficit developing in that window.

Counter-evidence held on record

Counter-evidence and confounding Confounding by indication is presumed: obese patients start with higher rates of low vitamin D, and the 6.6% placebo rate shows the background. Low BMD or fracture is not vitamin D deficiency (Hard Rule 2) and no fracture outcome is claimed here. The Gotfredsen trial was small and its vitamin D result was read only as a portal summary. Framing caution Label advice is a fat-soluble multivitamin at least 2 hours before or after orlistat [1]. The adolescent pilot suggests a multivitamin may not fully offset the effect [4], which supports monitoring, not a dose recommendation. No dose is given here.

Limits on what this shows

• Null findings: Oxygenated carotenoids unchanged [5]. No functional marker (such as dark adaptation or retinol status) was measured in either source, and serum retinol was unchanged in adolescents [4].
• At-risk subgroups: Unsupplemented users; people relying on carotenoid-rich foods for vitamin A activity.

Regulatory status

Beta-carotene is named in the US label warning and vitamin table [1].

Population evidence

Label table, unsupplemented adults: beta-carotene low in 6.1% on orlistat versus 1.7% on placebo [1]. Sundl 2007 [5]: prospective intervention in 6 patients with BMI 30 or more, measurements at baseline, 3 and 4.5 months; alpha-carotene fell 45% (P=0.006), beta-carotene fell 32% (P=0.013), lycopene fell then recovered, oxygenated carotenoids (beta-cryptoxanthin, lutein/zeaxanthin) were unchanged (read through an aggregator page and summarizer, journal page not opened).

Mechanism

Plausible: the abstract states the fall was in the "highly lipophilic hydrocarbon carotenoids", alpha- and beta-carotene, consistent with reduced fat absorption [5]; the mechanism was not tested directly.

Why not red

The second source has 6 participants, there is no functional or clinical endpoint, and carotenoids are not an essential nutrient with a defined deficiency state.

Counter-evidence held on record

Counter-evidence and confounding The 6-person study had no placebo group, so a change in carotenoid-rich food intake during treatment is a competing explanation that [5] does not exclude. Framing caution This is a circulating-level observation, not a vitamin A deficiency claim. Retinol status is graded separately (yellow) and was not reduced in the adolescent study [4].

Limits on what this shows

• Null findings: In the case report the 24-hour urine oxalate was normal despite biopsy crystals [13]. Incidence is not quantified in the sources read.
• At-risk subgroups: Existing or at-risk kidney disease, volume depletion, prior stones [1][2].

Regulatory status

US label: "Acute oxalate nephropathy after treatment with XENICAL has been reported in patients with or at risk for renal disease", and cases of oxalate nephrolithiasis and nephropathy with renal failure are in the warnings [1]. EMA SmPC: use "may be associated with hyperoxaluria and oxalate nephropathy leading sometimes to renal failure", particularly with underlying kidney disease [2].

Population evidence

No population-level incidence study was opened. Case report, Chaudhari 2013 [13]: a 56-year-old woman, 70 lb intentional weight loss over 18 months, presented with fatigue and acute kidney injury (creatinine 6.6 mg/dL); biopsy showed tubular oxalate crystals; creatinine had improved only to 5.7 mg/dL after hydration and did not recover at 3 months; the authors cite 3 earlier orlistat cases (via summarizer). The review by Filippatos 2008 [12] reports rare acute kidney injury, potentially from increased oxalate absorption secondary to fat malabsorption.

Mechanism

Named but described only as "potentially" in the review [12]: increased oxalate absorption secondary to fat malabsorption. The mechanism is not established in the sources read.

Why not red

The two regulatory labels are the only Tier A sources and neither quantifies oxalate excretion; they are not independent clinical measurements. Incidence and urinary oxalate data were not retrieved.

Counter-evidence held on record

Counter-evidence and confounding Rapid large weight loss, prior kidney disease and dehydration are competing contributors to kidney injury. The normal 24-hour urine oxalate in the single case [13] shows the urinary marker may not capture the event. Framing caution This is an excess/retention and toxicity risk. Supplementation is not the remedy and nothing here implies a nutrient should be added. Kidney function is a prescriber matter.

Limits on what this shows

• Null findings: No significant change in prothrombin time in trials [1]; the adolescent decline was nonsignificant [4].
• At-risk subgroups: Patients on warfarin or other vitamin K antagonists, patients with other fat malabsorption or poor vitamin K intake.

Regulatory status

US label: vitamin K absorption may be decreased; postmarketing reports of decreased prothrombin, increased INR and unbalanced anticoagulation in patients on warfarin, so coagulation parameters should be monitored (read through a summarizer) [1]. EMA SmPC: monitor coagulation in patients on oral anticoagulants [2].

Population evidence

Label clinical trials: "vitamin K levels tended to decline" while prothrombin time was unchanged [1]. McDuffie 2002 [4]: nonsignificant decrease in serum vitamin K in 17 adolescents on orlistat plus multivitamin. Vitamin K was not in the label low-vitamin incidence table that covers A, D, E and beta-carotene.

Mechanism

Named and plausible: vitamin K1 is fat-soluble and absorbed with dietary fat [1][2].

Direction check

The warfarin finding is a drug-drug pharmacodynamic interaction (Hard Rule 4), not a vitamin K deficiency in otherwise healthy users. Three published vitamin K deficiency coagulopathy case reports opened during searching did not involve orlistat and are not used [20].

Counter-evidence held on record

Counter-evidence and confounding The Tier A data show a nonsignificant trend only. The label itself does not report vitamin K deficiency incidence for this drug. Framing caution A monitoring prompt for anticoagulated patients, not a deficiency claim. Do not advise vitamin K supplementation from this entry; it would also interact with warfarin.

Limits on what this shows

• Null findings: Retinol absorption and serum levels unchanged [4]; levels normal [11]; pediatric supplemented low-vitamin rates 1.5% or lower [1].
• At-risk subgroups: Unsupplemented users with low intake; no orlistat-specific subgroup data found.

Regulatory status

Vitamin A is named in the US label vitamin table and the EMA SmPC warning [1][2].

Population evidence

Label, unsupplemented adults, years 1 to 2: low vitamin A 2.2% versus 1.0% [1]. McDuffie 2002 [4]: acute absorption of retinol not significantly altered and serum vitamin A unchanged in 17 adolescents on a multivitamin. Hollander 1998 [11]: levels generally normal.

Mechanism

Plausible through fat malabsorption, but the one direct retinol absorption test in an orlistat cohort was null [4].

Why yellow, not orange

The label difference is 1.2 percentage points and significance was not stated in the text read; the only functional-level measurement was null. A real deficit with orlistat in the cohort is not demonstrated.

Counter-evidence held on record

Counter-evidence and confounding Placebo rate 1.0% and the large baseline overlap make attribution uncertain. Carotenoid fall (orange entry) is not retinol deficiency. Framing caution Do not read the carotenoid finding as vitamin A deficiency. No dose recommended.

Limits on what this shows

• Null findings: No fall in muscle phospholipid omega-3, EPA, DHA or linoleic acid on orlistat [23]. No case or trial of essential fatty acid deficiency on orlistat was found. A PubMed listing for orlistat and essential fatty acids returned only unrelated records (cancer, antiviral and fatty acid synthase work).
• At-risk subgroups: None identified. Very low fat intake while on orlistat is a theoretical modifier, untested in the sources read.

Regulatory status

Neither the US label text read nor the EMA SmPC mentions essential fatty acids; both state the fat-absorption reduction of about 30% [1][2].

Population evidence

Tier A (orlistat in cohort) but indirect: Cruz-Hernandez et al., J Lipid Res 2016;57:2208-2216 [22], double-blind trial in 45 obese volunteers given EPA 500 mg and DHA 300 mg daily as monoacylglycerol or triacylglycerol oil, with orlistat used to induce lipid malabsorption. Abstract-level read: monoacylglycerol oil gave erythrocyte EPA and DHA 72% and 24% higher at 21 days, plasma EPA 56% higher, and a 55% larger chylomicron EPA area under the curve than triacylglycerol oil, and the authors concluded the monoacylglycerol form needs minimal enzymatic digestion. The abstract as read compares oil forms, not orlistat versus no orlistat, and reports no linoleic or alpha-linolenic acid, so it supports plausibility that lipase inhibition limits triacylglycerol-form omega-3 delivery without quantifying a deficit. Tier A, null direction: Haugaard et al., Lipids Health Dis 2009 [23], double-blind pilot, 9 obese adults (orlistat 120 mg three times daily n = 5, placebo n = 4) over a 24-week maintenance phase after a very low calorie diet. Skeletal muscle phospholipid total omega-3 rose 24% and DHA 35% overall; DHA rose 51% on orlistat versus 17% on placebo (p = 0.12), EPA 34% versus 32%, and linoleic acid changed +3.1% (not significant). The authors read the DHA trend as weight-loss related.

Mechanism

Named and plausible in principle: lipase inhibition reduces hydrolysis and absorption of dietary triacylglycerol fatty acids, including polyunsaturated ones [1][2][22]. Not shown to change essential fatty acid status.

Counter-evidence held on record

Counter-evidence and confounding The Haugaard study is tiny, measures muscle rather than plasma or erythrocyte fatty acids, and had weight loss and diet as confounders; the orlistat-versus-placebo split is underpowered. Eicosapentaenoic and docosahexaenoic acids are not strictly essential, and the trial tested supplemental oil. Reduced dietary fat absorption is the intended effect (Hard Rule 2). Full texts of [22] were not read, so orlistat versus no-orlistat contrasts inside it are unknown. Framing caution A mechanistic and indirect note only. It supports no claim that orlistat users are deficient in omega-3 or omega-6 and no supplement advice.

What changed

Oxygen delivery/utilization moved to yellow on one orlistat case report of macrocytic anemia with thrombocytopenia [21]. Essential fatty acids moved to yellow on a lipid-malabsorption-model trial [22] with a null status measurement [23]. Both are Tier A or B sources with orlistat in the cohort, opened this session at abstract or summary level through summarizing fetch tools.

Residual gaps (still tooling-limited)

No controlled or cohort measurement of hemoglobin, hematocrit or ferritin on orlistat was retrieved: a PubMed listing for orlistat with anemia, hemoglobin and iron terms returned 429 and was not repeated, and OpenAlex and Crossref returned 429. No plasma or erythrocyte linoleic or alpha-linolenic acid measurement on orlistat was retrieved; the full text of [22] and its orlistat versus no-orlistat results were not opened, and a ClinicalTrials.gov record NCT01414465 (orlistat and fatty acid composition in obese females) returned only page metadata. Re-check these when PubMed, PMC and ClinicalTrials.gov results access is restored.