Letrozole

An aromatase inhibitor that lowers estrogen, FDA-approved for hormone receptor-positive breast cancer after menopause.

psilodex.org/m/letrozole · data v2026.10.05

Clinical contraindication: None listed; No label contraindication covering psilocybin was found. This is not a finding that the combination has been shown to be without risk.
Psilocybin evidence: No psilocybin data
Half-life: ~2 days; Approximate, in adults. Source under Interaction below.

Named in state rules?

Not namedColorado Condition rules (3)

Not namedOregon

PendingNew Mexico

Cite asPsilodex, “Letrozole”, v2026.10.05. psilodex.org/m/letrozole

Clinical data and state rules are separate facts. Both are shown; neither is a decision.

What it is used for

FDA status

FDA-approved

FDA-approved for

Adjuvant treatment of hormone receptor-positive early breast cancer (postmenopausal)
Extended adjuvant treatment of early breast cancer after 5 years of tamoxifen (postmenopausal)
Advanced or metastatic breast cancer (postmenopausal)

Sources [1]

01 Interaction with psilocybin

Not studied with psilocybin; no linking mechanism is described. Separately, it lowers estrogen and can cause tiredness, dizziness and bone loss.

Detail Letrozole has no known interaction with psilocybin. Separately, it lowers estrogen, and its label reports fatigue, dizziness and sleepiness, bone loss and raised cholesterol. Sources [1]

Human data with psilocybin: No psilocybin data; based on its label
Half-life: ~2 days (FDA label, checked 2026-10-04) Steady state after 2–6 weeks of daily dosing.

Evidence types on this record

No psilocybin dataNo psilocybin data: no human data with psilocybin or another classic psychedelic; the text draws on the medication's own pharmacology and its label or reference facts

02 Pharmacology relevant to psilocybin

None listed

No pharmacology properties of concern are listed for this record.

03 State rules

Plain-language summary · official text governs

CO4 CCR 755-1

Not namedCondition rules (3)

No provision names this medication or its class.

Colorado · checked 2026-10-04

OROAR 333-333

Not named

No provision names this medication or its class.

Oregon · checked 2026-10-04

NM7.35.3 NMAC (proposed)

Pending

New Mexico's clinical rules (proposed 7.35.3 NMAC) are not final. No provision naming this medication has been found.

New Mexico · checked 2026-10-04

04 Conditions to ask about

Screening items in state rules

This medication is usually taken for a condition. State rules screen for some conditions directly, so the medication is a prompt to ask about them. Confirm with the participant; never assume a condition from the medication.

Cancer history
- CO 2.5(A)(2) · Clinical Facilitator licensees
- CO 6.16(F)(2)(a) · Facilitators without a clinical facilitator license
- CO 6.16(F)(1) · All licensees

05 Sources

FEMARA (letrozole) tablets (Novartis) · FDA label (DailyMed) — 5.4 "Because fatigue, dizziness, and somnolence have been reported with the use of Femara" | 5.1 "Use of Femara may cause decreases in bone mineral density (BMD)." | 12.3 "Letrozole’s terminal elimination half-life is about 2 days and steady-state plasma concentration after daily 2.5 mg dosing is reached in 2-6 weeks."
Halman A, Kong G, Sarris J, Perkins D. Drug–drug interactions involving classic psychedelics: a systematic review. J Psychopharmacol 2024;38(1):3–18. — no reported interaction
Sarparast A, Thomas K, Malcolm B, Stauffer CS. Drug-drug interactions between psychiatric medications and MDMA or psilocybin: a systematic review. Psychopharmacology 2022;239(6):1945–1976. — no reported interaction

Record history

v2026.10.02First published.
2026-10-04Last reviewed against its sources.

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