Drug & supplement interaction

Weight Watchers Diet + Letrozole

Letrozole brand name: Femara.

No Known Interaction

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Updated June 2026 · Pair last verified Sep 13, 2026

The bottom line No known interaction

We found no known interaction between Weight Watchers Diet and Letrozole in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first.

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Interaction report

Weight Watchers Diet and Letrozole

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Letrozole and Weight Watchers Diet in our sources. This does not guarantee that the combination is completely free of risk — research on Weight Watchers Diet alongside specific medications may be limited.

Weight Watchers Diet is an eating pattern rather than something you take. Ask your pharmacist or doctor before changing how you eat while on a prescribed medicine: some medicines are dosed around meals, and a change in diet can change how they work. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

Weight Watchers Diet safety at a glance

Weight Watchers Di... overall Use caution Generally safe for most healthy adults, but check with a clinician if you have health conditions or take medications.

Pregnancy Use caution Weight loss is usually not advised during pregnancy; speak with your doctor about appropriate nutrition.

Breastfeeding Use caution Calorie restriction may affect milk supply, so discuss any diet plan with your healthcare provider first.

Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Letrozole and Weight Watchers Diet? Ask Dr. Brian Staiger, PharmD, BCPS directly ›

How we checked

Why No Interaction Is Listed for Letrozole

Interactions in our licensed database are recorded against drug classes, not just single drug names. Letrozole is filed under 4 classifications — including aromatase inhibitors, cytochrome p450 2c19 (cyp2c19) inhibitors, cytochrome p450 3a4 (cyp3a4) substrates. Weight Watchers Diet has documented interactions with 1 drug class — the most serious being antidiabetes drugs (moderate) — and none of Letrozole’s classifications are among them.

Classification data comes from our licensed Natural Medicines dataset. A medication can belong to classes beyond those recorded there, so this describes how the check was run — it is not a safety guarantee.

Keep it in perspective

Weight Watchers Diet Does Interact With Other Medications

Weight Watchers Diet has 86 moderate known drug interactions in our database — Letrozole isn’t one of them. If you take anything else, check it against the full list below.

Moderate 86 No known interaction 2,744 (incl. Letrozole)

Taking anything else?

Check Another of Your Medications Against Weight Watchers Diet

Covers the 2,830 medications we’ve checked against Weight Watchers Diet. Pick one to open its full report.

What to actually watch for

What Letrozole’s Own FDA Label Lists

This is not an interaction — none of it involves Weight Watchers Diet. These are the most notable effects listed in the ADVERSE REACTIONS section of Letrozole’s own FDA label, for the medication by itself. Knowing the drug’s own list makes it easier to work out the likely cause if something new turns up while you follow Weight Watchers Diet and take the medicine. One of them is worth acting on rather than waiting out — marked below.

Bleeding or bruising Worth acting on
Flushing
Sweating
Joint pain
Muscle pain
Swelling
Tiredness
Dizziness
Headache
Nausea

From the ADVERSE REACTIONS section of the FDA label for Letrozole. Read the label on DailyMed › Weight Watchers Diet’s licensed record lists no adverse effects our clinical vocabulary could match, so there is no Weight Watchers Diet side to compare — that is a limit of the record, not a statement that Weight Watchers Diet has no side effects.

From our Q&A

Questions About Weight Watchers Diet or Letrozole

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Weight Watchers Diet or Letrozole, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Letrozole

This page covers Weight Watchers Diet only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Letrozole page lists 142 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Grapefruit (major), St. John's Wort (major), 7-methoxyflavone (moderate) and Acacia Rigidula (moderate).

By severity: 3 major · 99 moderate · 40 minor.

From our pharmacist’s overview on the Letrozole page

“Letrozole (Femara) is prescribed to keep hormone-driven breast cancer from returning, so a supplement that shifts its blood level can quietly undercut treatment. Give this list of 142 ingredients genuine respect, and learn the three major entries first.”

Reviewed by 2 · Jul 18, 2026

Open the Letrozole interaction page

How much people look this up

Where Weight Watchers Diet and Letrozole Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Weight Watchers Diet

Steady interest

#1,094 of 1,452 supplements looked up here in the last 7 days

29 days ago today

Medication Letrozole

Top 5%

#50 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Where does our data come from?

Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Weight Watchers Diet reference on this page ↓
Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Weight Watchers Diet and Letrozole records this page draws on were last updated June 22, 2026.
What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.

Data structure & sourcing designed and verified by Dr. Brian Staiger, PharmD, BCPS.

Eating pattern

About Weight Watchers Diet

What is Weight Watchers Diet?

Weight loss
Weight maintenance
Building healthier eating habits
Behavioral support for diet change
General wellness and lifestyle improvement

Weight Watchers (now called WW) is a commercial weight-loss program built around a points system, food tracking, and group or online support rather than a pill or herbal product. Research generally shows it can help people lose a modest amount of weight and keep some of it off, especially when combined with regular activity. Talk with your doctor or pharmacist before starting any weight-loss plan, particularly if you have a medical condition.

Not applicable (this is a commercial weight-management program, not a plant or supplement) · Structured eating plan with a points-based food system, app, group or online support, and coaching

An interaction check asks whether these two react with each other — it does not ask whether Weight Watchers Diet is a good idea for someone in your situation. Here is what our Weight Watchers Diet record says about it on its own.

Weight Watchers Diet: dosing

There is no pill or standardized dose for Weight Watchers, since it is a behavioral eating program. Instead, you follow the program's points budget and tracking system as set up in the app or plan you select.The right calorie or points target depends on your age, sex, weight, activity level, and goals, and the program personalizes this for you.

From our Weight Watchers Diet monograph — the full record covers uses, side effects and every documented interaction.

Read the full Weight Watchers Diet monograph & all interactions

Medication

About Letrozole

What Is Letrozole Used For?

Brand name: Femara

Letrozole (brand name Femara, or available as generic letrozole tablets) is used to treat breast cancer in postmenopausal women whose tumors are hormone receptor positive — meaning the cancer feeds on estrogen. It is used in several situations: as an adjuvant treatment (therapy given after primary treatment to reduce the risk of the cancer returning) for early breast cancer, and as extended adjuvant treatment for women who have already completed five years of tamoxifen therapy.

Femara and letrozole tablets are also used as first-line or second-line treatment for locally advanced or metastatic (spread to other areas) breast cancer in postmenopausal women, including cases where the cancer has progressed after other anti-estrogen therapy.

See full Letrozole drug information

Keep checking

Other Drugs & Weight Watchers Diet

Browse every other medication we’ve checked against Weight Watchers Diet — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major

86Moderate

0Minor

2,743No known interaction

86 Moderate 2,743 No interaction

Moderate

86 interactions

Showing 60 of 86 moderate interactions — see all 86 on the Weight Watchers Diet page.

No interaction 2,743 drugs checked — show the list

We also checked Weight Watchers Diet against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,743 medications checked with no known interaction — see the full Weight Watchers Diet list.

See the full Weight Watchers Diet interactions page

See every supplement checked against Letrozole, ranked by severity

Evidence & sources

Weight Watchers Diet References

The 1 references that drive our Weight Watchers Diet monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

O'Neil PM, Miller-Kovach K, Tuerk PW, et al. Randomized controlled trial of a nationally available weight control program tailored for adults with type 2 diabetes. Obesity (Silver Spring). 2016;24(11):2269-2277. PubMed

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Following Weight Watchers Diet While Taking Letrozole: Common Questions

Is it safe to follow Weight Watchers Diet while taking Letrozole?

We do not list a known interaction between Weight Watchers Diet and Letrozole. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.

How was the Weight Watchers Diet and Letrozole combination checked?

Interactions in our licensed database are recorded against drug classes. Letrozole is filed under 4 classifications, and Weight Watchers Diet has documented interactions with 1 drug class — none of Letrozole's classifications are among them. A medication can belong to classes beyond those recorded in our dataset, so this describes how the check was run rather than guaranteeing safety.

Does Weight Watchers Diet interact with any other medications?

Yes. Weight Watchers Diet has 86 documented drug interactions in our database — Letrozole is simply not one of them. If you take anything else, it is worth checking each one; they are all listed on this page.

Does Letrozole interact with any supplements?

Yes. Letrozole has documented interactions with 142 supplements in our database — Weight Watchers Diet is not one of them. The Letrozole interaction page linked on this page lists every one, ranked by severity.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Where next

Keep Exploring

Weight Watchers Diet monograph Uses, safety profile, and every drug interaction in one place Letrozole drug information The full plain-English guide to this medication Letrozole supplement interactions Every supplement checked against Letrozole, ranked by severity Supplement interaction checker Check any supplement or product against your medications Browse medications A–Z Every drug we’ve checked against herbs & supplements References The 1 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Letrozole and Weight Watchers Diet?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.