Drug Interaction Report

Orlistat and Venlafaxine: Interaction Details

Name: Orlistat and Venlafaxine Interaction
Creator: Dr. Brian Staiger, PharmD, BCPS

A pharmacist-reviewed analysis of the Orlistat and Venlafaxine interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Aug 9, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Venlafaxine

No brand names on record

Orlistat

Alli Alli® Xenical Xenical®

Medically reviewed by

Dr. Brian Staiger, PharmD, BCPS

Updated Aug 9, 2026

Editorial policy · Data sources

Interaction severity

Major

Potentially serious — often needs a change or close monitoring.

Minor

Moderate

Major

Contraindicated

How we grade severity & evidence

Severity levels

Contraindicated: These should generally not be used together.
Major: Potentially serious — often needs a change or close monitoring.
Moderate: Can be significant — usually manageable with monitoring.
Minor: Usually limited clinical impact.

Evidence grades

Established: Well documented — supported by controlled studies or strong clinical data.
Probable: Good supporting evidence, though not definitively proven.
Suspected: Some evidence suggests this interaction, but it is not well established.
Possible: Limited or conflicting evidence; the interaction may occur.
Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.

Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.

Of 144 documented Orlistat interactions, 139 are rated major — including this one.

Worried about symptoms right now? Contact your pharmacist or prescriber, or call Poison Control at 1-800-222-1222 (US). Call 911 for an emergency.

Onset

unspecified

Evidence

theoretical

Severity

Major

What happens

An increase risk of adverse events

Interaction Deep Dive

The safety and efficacy of concomitant use of venlafaxine and an agent used for weight loss has not been established and therefore is not recommended¹.

Why it happens (mechanism)

Additive effects

Common questions

Can I take Orlistat and Venlafaxine together?

An increase risk of adverse events Always confirm with your pharmacist or prescriber before making any change.

How serious is the Orlistat and Venlafaxine interaction?

It is rated major. Potentially serious — often needs a change or close monitoring.

How quickly could this interaction happen?

The documented onset is "unspecified". The timing of this interaction is not well characterized.

How strong is the evidence for this interaction?

The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.

From our Q&A

Real reader questions about these medications, each personally answered by our pharmacist:

Questions for your pharmacist

Does my dose of Orlistat or Venlafaxine need adjusting while I take them together?
What symptoms should prompt me to call you or my prescriber right away?
Does the timing of my doses matter for this combination?
Is there a safer alternative to one of these medications for me?

References (1)

Product Information: EFFEXOR XR(R) oral extended-release capsules, venlafaxine oral extended-release capsules. Wyeth Pharmaceuticals Inc (per FDA), Philadelphia, PA, 2022. DailyMed

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Venlafaxine

Keep reading about Venlafaxine

All Venlafaxine interactions (130)

Also serious with: Metoclopramide Nasal Spray Metoclopramide Injection Ketoconazole Topical Linezolid Injection

Orlistat

Keep reading about Orlistat

All Orlistat interactions (144) Orlistat drug information

Also serious with: Brivaracetam Midazolam Nasal Spray Zonisamide Diazepam Nasal Spray

Beyond drug–drug

These medications also interact with supplements

Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:

Venlafaxine + Activated Charcoal American Hellebore Arsenic Cesium Ephedra Grapefruit Lithium Sida Cordifolia + 102 more

Orlistat + Activated Charcoal Coffee Charcoal European Mandrake Fish Oil Glucomannan Guar Gum Gum Arabic Slippery Elm + 10 more

major · moderate · minor — check everything you take with our drug–supplement interaction checker.

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A message from HelloPharmacist

About our interaction database: depth, not breadth

HelloPharmacist doesn't license one of the big commercial interaction databases, so what you'll find here is not a complete list of every known drug interaction. Instead, each entry is researched, analyzed, and written up individually — documented from the published literature, reviewed by a pharmacist, and cited so you can check every source yourself.

If a combination isn't listed here, it means we haven't documented it yet — never that it's safe. For screening a full medication list, we recommend pairing this site with a comprehensive tool like the Drugs.com Interaction Checker and, most importantly, a review by your own pharmacist. For a deep, plain-English, fully sourced explanation of a specific documented interaction — that's exactly what we built this for.

This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.