Tamoxifen

A selective estrogen receptor modulator for treating estrogen receptor-positive breast cancer and lowering breast cancer risk.

psilodex.org/m/tamoxifen · 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: 5–7 days; Approximate, in adults. Source under Interaction below.

Named in state rules?

Not namedColorado Condition rules (3)

Not namedOregon

PendingNew Mexico

Cite asPsilodex, “Tamoxifen”, v2026.10.05. psilodex.org/m/tamoxifen

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

Estrogen receptor-positive metastatic breast cancer
Adjuvant treatment of early estrogen receptor-positive breast cancer
Ductal carcinoma in situ (DCIS) after surgery and radiation, to reduce invasive breast cancer risk
Reducing breast cancer incidence in women at high risk

Sources [1][2]

Other safety

Boxed warning: uterine cancers, stroke and pulmonary embolism, including fatal cases; the label also reports a marked increase in warfarin's anticoagulant effect.

About the medication itself, separate from any interaction with psilocybin.

Sources [1]

01 Interaction with psilocybin

No known interaction with psilocybin; both may use the same liver enzyme. Separately, its label reports liver problems and high blood calcium in some people.

Detail Not studied with psilocybin, and no mechanism linking them has been described. CYP2D6 (a liver enzyme) is the key enzyme forming tamoxifen's potent metabolite endoxifen. In lab studies, CYP2D6 also metabolized psilocin (Thomann 2024), so the two may share this enzyme. However, psilocin is eliminated mainly by glucuronidation and conversion to 4-HIAA. Separately, the label reports liver abnormalities, including rare severe cases, and high blood calcium in some people with bone metastases. Sources [1][3]

Human data with psilocybin: No psilocybin data; based on how it works and its label
Half-life: 5–7 days (N-desmethyl metabolite ~14 days) (FDA label, checked 2026-10-04)

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

2 listed · counted on reports

Dehydration or electrolyte risk: Can cause dehydration or shifts in sodium or potassium. Sources [1]
Liver injury: The label or source warns of liver injury, from raised liver enzymes to liver failure. Liver disease also affects how the body clears psilocin. Sources [1]

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

SOLTAMOX (tamoxifen citrate) oral solution (Mayne) · FDA label (DailyMed) — Liver injury: 5.4 Non-Malignant Effects on the Liver "a spectrum of more severe liver abnormalities including fatty liver, cholestasis, hepatitis and hepatic necrosis. Some of these serious cases included fatalities." | Dehydration or electrolyte risk: 5.6 "hypercalcemia has been reported in some breast cancer patients with bone metastases within a few weeks of starting treatment with tamoxifen" | 12.3 "it is the key enzyme that catalyzes the formation of endoxifen from N-desmethyltamoxifen" | Boxed Warning "Serious and life-threatening events from the use of SOLTAMOX include uterine malignancies, stroke, and pulmonary embolism" | 7.2 "A marked increase in anticoagulant effect may occur when tamoxifen is used in combination with warfarin." | "terminal elimination half-life of about 5 to 7 days" "suggesting a half-life of approximately 14 days for this metabolite"
Tamoxifen Citrate Tablets (Mylan) · FDA label (DailyMed)
Thomann J, Kolaczynska KE, Stoeckmann OV, et al. In vitro and in vivo metabolism of psilocybin’s active metabolite psilocin. Front Pharmacol 2024;15:1391689. — Abstract: "recombinant CYP2D6 and CYP3A4 enzymes metabolized nearly 100% and 40% of psilocin, respectively." "In conclusion, MAO-A, CYP2D6, and CYP3A4 are involved in psilocin's metabolism."
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.

Report an error in this record →