Tamoxifen

For an informed discussion with your doctor or pharmacist. This information collection is not a clinically validated interaction checker. Missing data do not establish safety. Do not change or stop prescribed medicines on the basis of this information. The findings apply to the specific conditions studied; laboratory and animal studies cannot be directly extrapolated to humans.

Active substance: Tamoxifen

Examples of brand names: Nolvadex [DE]

ATC code: L02BA01

Main use (for orientation): Breast cancer

Documented research summary

Clinical CBD-related endoxifen reduction remains decisive (CL16/17); preclinical synergy cannot negate this pharmacokinetic question. A small low-dose study is not a general assurance of safety.

Uncertainties and limitations

Historical US SPL from 2007; identity verified through DESCRIPTION as a single-ingredient tamoxifen citrate tablet despite an empty structured ingredient list; no claim of currency.

Shared enzymes must not be equated with clinical evidence of an interaction; CBD/THC findings cannot be extrapolated to other cannabinoids.

Separately recorded findings

8 separately recorded findings. Each statement applies to its documented study context.

CBD – clinically studied

Finding ID: B0040

Type of result: Positive finding / indication

Observation: Endoxifen AUC −12.6% (90% CI −18.7 to −6.1%); within predefined bioequivalence limits.

Mechanism: Reduced bioactivation plausible

Study type: Open-label single-arm pharmacokinetic crossover study

Context studied: Pharmacokinetic n=15; CBD oil approximately 50 mg/day sublingually for 4 weeks; THC <0.05%.

Clinical interpretation: Small pharmacokinetic effect; long-term relevance unresolved

Limitations and uncertainties: Endoxifen ≥16 nM required; four weeks, no conclusion about recurrence/survival. Bioequivalence applies to the primary overall AUC, not indiscriminately to all endpoints: endoxifen Cmin and Cmax confidence intervals cross the lower limit. Exploratory CYP2D6 intermediate metabolisers n=8: AUC −20.8% (90% CI −26.4 to −14.8); extensive metabolisers n=7: −2.2% (−11.1 to +7.6). Small subgroups, no established phenotype effect.

Original sources for this finding: CBD-oil as a potential solution in case of severe tamoxifen-related side effects [CL16]

CBD – clinically studied

Finding ID: B0041

Type of result: No / minor effect under the conditions studied

Observation: Overall sample n=15: tamoxifen AUC0–24h −2.8% (90% CI −7.7 to +2.4), Cmin −7.2% (−14.1 to +0.4), Cmax −1.2% (−8.2 to +6.4); no significant difference.

Mechanism: Parent-substance pharmacokinetics

Study type: Open-label single-arm pharmacokinetic crossover study

Context studied: Same sample of n=15.

Clinical interpretation: Parent-substance null finding

Limitations and uncertainties: Consider the endoxifen finding separately.

Original sources for this finding: CBD-oil as a potential solution in case of severe tamoxifen-related side effects [CL16]

CBD – clinical signals

Finding ID: B0042

Type of result: Positive finding / indication

Observation: After CBD discontinuation: endoxifen +18.75%, N-desmethyltamoxifen +9.24%.

Mechanism: CYP3A4/CYP2D6 inhibition suspected

Study type: Case report

Context studied: n=1; CBD 40 mg/day; 60-day washout.

Clinical interpretation: Unclear; possible efficacy relevance

Limitations and uncertainties: No causality or cancer prognosis established; product composition not fully assessed.

Original sources for this finding: Reduction in Tamoxifen Metabolites Endoxifen and N-desmethyltamoxifen With Chronic Administration of Low Dose Cannabidiol: A CYP3A4 and CYP2D6 Drug Interaction [CL17]

CBD – laboratory and animal studies

Finding ID: B0187

Type of result: Preclinical evidence

Observation: Enhanced cell apoptosis and tumour-growth inhibition in combination.

Mechanism: CREB/ERα

Study type: Cell / animal experiment, abstract read

Context studied: MCF7/T47D and xenograft; not an endoxifen pharmacokinetic test.

Clinical interpretation: Not clinically validated

Limitations and uncertainties: No human drug–drug interaction; not a treatment recommendation.

Original sources for this finding: Cannabidiol enhances tamoxifen efficacy via CREB-mediated suppression of ERα signaling in ER-positive breast cancer cells. [BMED42210419]

CBD – laboratory and animal studies

Finding ID: B0188

Type of result: Preclinical evidence

Observation: Synergistic cytotoxicity in T-ALL cells.

Mechanism: Cyclophilin D/mitochondrial calcium homeostasis

Study type: Cell / animal experiment, abstract read

Context studied: Not breast-cancer patients; TAM→CBD sequence mechanistically relevant.

Clinical interpretation: Not clinically validated

Limitations and uncertainties: No human drug–drug interaction; not a treatment recommendation.

Original sources for this finding: Tamoxifen Sensitizes Acute Lymphoblastic Leukemia Cells to Cannabidiol by Targeting Cyclophilin-D and Altering Mitochondrial Ca2+ Homeostasis. [BMED34445394]

THC/cannabis extract – laboratory and animal studies

Finding ID: B0189

Type of result: Preclinical evidence

Observation: Additive cell-culture effect; no positive or negative interaction observed in vivo.

Mechanism: Antiproliferation

Study type: Cell / animal experiment, abstract read

Context studied: Breast-cancer models; pure THC and botanical preparation distinguished; abstract summarises several partners.

Clinical interpretation: Not clinically validated

Limitations and uncertainties: No human drug–drug interaction; not a treatment recommendation.

Original sources for this finding: Appraising the "entourage effect": Antitumor action of a pure cannabinoid versus a botanical drug preparation in preclinical models of breast cancer. [BMED29940172]

CBD/THC (separate tests) – laboratory and animal studies

Finding ID: B0190

Type of result: Preclinical evidence

Observation: No synergy with tamoxifen observed; cannabinoid effect strongly serum-dependent.

Mechanism: C6 glioma cell viability

Study type: Cell / animal experiment, abstract read

Context studied: Rat C6 cells; not a pharmacokinetic/patient test.

Clinical interpretation: Not clinically validated

Limitations and uncertainties: No human drug–drug interaction; not a treatment recommendation.

Original sources for this finding: Serum-dependent effects of tamoxifen and cannabinoids upon C6 glioma cell viability. [BMED11108795]

THC – laboratory and animal studies

Finding ID: B0191

Type of result: Preclinical evidence

Observation: Tamoxifen altered THC effects in ovariectomised/oestrogen-treated rats; context-dependent pre/postsynaptic markers.

Mechanism: Oestrogen modulation of dopaminergic signals

Study type: Cell / animal experiment, abstract read

Context studied: Mechanistic receptor-blockade experiment, not a breast-cancer interaction; additional context 19912874.

Clinical interpretation: Not clinically validated

Limitations and uncertainties: No human drug–drug interaction; not a treatment recommendation.

Original sources for this finding: delta 9-Tetrahydrocannabinol affects mesolimbic dopaminergic activity in the female rat brain: interactions with estrogens. [BMED8103663]; Estrogenic modulation of delta(9)-Tetrahydrocannabinol effects on nigrostriatal dopaminergic activity in the female rat brain. [BMED19912874]

References and access status

[V2_LABEL_D0395] TAMOXIFEN CITRATE (TAMOXIFEN CITRATE) TABLET [ANDRX PHARMACEUTICALS, INC.]

Original source / bibliographic reference

Authors: Andrx Pharmaceuticals, Inc.

Year: 2007

Source type: Official US SPL / DailyMed

Source access – 23 October 2026: Source destination was accessible when checked.

Bibliographic attribution or source identity cross-checked.

[CL16] CBD-oil as a potential solution in case of severe tamoxifen-related side effects

Original source / bibliographic reference

Authors: Buijs SM; Braal CL; Buck SAJ; van Maanen NF; van der Meijden-Erkelens LM; Kuijper-Tissot van Patot HA; Oomen-de Hoop E; Saes L; van den Boogerd SJ; Struik LEM; van Rossum-Schornagel QC; Mathijssen RHJ; Koolen SLW; Jager A

Year: 2023

Source type: Open-label single-arm pharmacokinetic crossover study

DOI: 10.1038/s41523-023-00570-x

PMID: 37543688

Source access – 23 October 2026: Source destination was accessible when checked.

Bibliographic attribution or source identity cross-checked.

[CL17] Reduction in Tamoxifen Metabolites Endoxifen and N-desmethyltamoxifen With Chronic Administration of Low Dose Cannabidiol: A CYP3A4 and CYP2D6 Drug Interaction

Original source / bibliographic reference

Authors: Parihar V; Rogers A; Blain AM; Zacharias SRK; Patterson LL; Siyam MA

Year: 2022

Source type: Case report

DOI: 10.1177/0897190020972208

PMID: 33191836

Source access – 23 October 2026: Source destination was accessible when checked.

Bibliographic attribution or source identity cross-checked.

[BMED42210419] Cannabidiol enhances tamoxifen efficacy via CREB-mediated suppression of ERα signaling in ER-positive breast cancer cells.

Original source / bibliographic reference

Authors: Kim BG, Kim O, Lee DY, Kim BR, Kim DY, Namgung Y, Bong JW, Kang S, Lee SI, Oh SC.

Year: 2026

Source type: Publication; title and abstract reviewed

DOI: 10.1186/s13578-026-01588-x

PMID: 42210419

Source access – 23 October 2026: Automated direct retrieval was restricted; this does not establish that the link is broken.

Bibliographic attribution or source identity cross-checked.

PubMed – bibliographic reference / abstract

PubMed Central – archived text

DOI – publisher access (access restrictions may apply)

[BMED34445394] Tamoxifen Sensitizes Acute Lymphoblastic Leukemia Cells to Cannabidiol by Targeting Cyclophilin-D and Altering Mitochondrial Ca2+ Homeostasis.

Original source / bibliographic reference

Authors: Olivas-Aguirre M, Torres-López L, Gómez-Sandoval Z, Villatoro-Gómez K, Pottosin I, Dobrovinskaya O.

Year: 2021

Source type: Publication; title and abstract reviewed

DOI: 10.3390/ijms22168688

PMID: 34445394

Source access – 23 October 2026: Automated direct retrieval was restricted; this does not establish that the link is broken.

Bibliographic attribution or source identity cross-checked.

PubMed – bibliographic reference / abstract

PubMed Central – archived text

DOI – publisher access (access restrictions may apply)

[BMED29940172] Appraising the "entourage effect": Antitumor action of a pure cannabinoid versus a botanical drug preparation in preclinical models of breast cancer.

Original source / bibliographic reference

Authors: Blasco-Benito S, Seijo-Vila M, Caro-Villalobos M, Tundidor I, Andradas C, García-Taboada E, Wade J, Smith S, Guzmán M, Pérez-Gómez E, Gordon M, Sánchez C.

Year: 2018

Source type: Publication; title and abstract reviewed

DOI: 10.1016/j.bcp.2018.06.025

PMID: 29940172

Source access – 23 October 2026: Automated direct retrieval was restricted; this does not establish that the link is broken.

Bibliographic attribution or source identity cross-checked.

PubMed – bibliographic reference / abstract

DOI – publisher access (access restrictions may apply)

[BMED11108795] Serum-dependent effects of tamoxifen and cannabinoids upon C6 glioma cell viability.

Original source / bibliographic reference

Authors: Jacobsson SO, Rongård E, Stridh M, Tiger G, Fowler CJ.

Year: 2000

Source type: Publication; title and abstract reviewed

DOI: 10.1016/s0006-2952(00)00492-5

PMID: 11108795

Source access – 23 October 2026: Automated direct retrieval was restricted; this does not establish that the link is broken.

Bibliographic attribution or source identity cross-checked.

PubMed – bibliographic reference / abstract

DOI – publisher access (access restrictions may apply)

[BMED8103663] delta 9-Tetrahydrocannabinol affects mesolimbic dopaminergic activity in the female rat brain: interactions with estrogens.

Original source / bibliographic reference

Authors: Bonnin A, Fernández-Ruiz JJ, Martín M, Rodríguez de Fonseca F, Hernández ML, Ramos JA.

Year: 1993

Source type: Publication; title and abstract reviewed

DOI: 10.1007/bf01244868

PMID: 8103663

Source access – 23 October 2026: Automated direct retrieval was restricted; this does not establish that the link is broken.

Bibliographic attribution or source identity cross-checked.

PubMed – bibliographic reference / abstract

DOI – publisher access (access restrictions may apply)

[BMED19912874] Estrogenic modulation of delta(9)-Tetrahydrocannabinol effects on nigrostriatal dopaminergic activity in the female rat brain.

Original source / bibliographic reference

Authors: Bonnin A, Ferández-Ruiz JJ, Martín M, De Fonseca FR, De Miguel R, Ramos JA.

Year: 1992

Source type: Publication; title and abstract reviewed

DOI: 10.1016/1044-7431(92)90028-z

PMID: 19912874

Source access – 23 October 2026: Automated direct retrieval was restricted; this does not establish that the link is broken.

Bibliographic attribution or source identity cross-checked.

PubMed – bibliographic reference / abstract

DOI – publisher access (access restrictions may apply)

Research as of 23 October 2026. Not all original full texts could be reviewed in full. Source accessibility and the strength of scientific evidence must be assessed separately. An accessible link does not establish medical approval; a bibliographic record with an abstract does not replace the original full text.

Drug search and explanation of the evidence · Guide: cannabinoids and medicines · Author and responsibility