Letrozole

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: Letrozole

Examples of brand names: Femara [DE]

ATC code: L02BG04

Main use (for orientation): Breast cancer

Documented research summary

CBD and CBN were each investigated with letrozole in ER-positive breast cancer cell models. No consistent additional antiproliferative benefit compared with letrozole alone; individual signalling pathways were altered. No clinical evidence of benefit/safety; no measured pharmacokinetic finding.

Uncertainties and limitations

Documented individual title/abstract review with selected relevant full texts; not an exhaustive worldwide systematic review and no independent human professional approval. Missing data do not establish safety. All 28 cannabinoids define the search scope, not 28 clinically studied pairs per active substance.

Separately recorded findings

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

CBD – laboratory and animal studies

Finding ID: B0470

Type of result: Context-specific finding

Observation: Letrozole plus CBD showed no additional viability or apoptosis benefit in this model.

Mechanism: Modulation of cell viability, apoptosis and ER/AR/ERK-dependent signalling pathways.

Study type: In-vitro breast cancer model, pharmacodynamics

Context studied: MCF-7aro cells; CBD 1/5 µM and aromatase inhibitors 10 µM, different hormonal conditions; relevant methods, results and discussion sections of the full text read.

Clinical interpretation: Applicability to humans is unresolved; preclinical endpoint, not clinical evidence of treatment efficacy or safety.

Limitations and uncertainties: No clinical cancer-treatment interaction or assurance of efficacy. Concentrations and hormonal conditions are decisive; viability must not be equated with apoptosis.

Original sources for this finding: Cannabidiol as a Promising Adjuvant Therapy for Estrogen Receptor-Positive Breast Tumors: Unveiling Its Benefits with Aromatase Inhibitors. [VF_P_37173983]

CBN – laboratory and animal studies

Finding ID: B0473

Type of result: Context-specific finding

Observation: CBN provided no additional benefit with letrozole in the model investigated.

Mechanism: Context-dependent combination of CBN with aromatase inhibitors.

Study type: Cell and spheroid models, pharmacodynamics

Context studied: Original abstract, breast cancer cell models.

Clinical interpretation: Applicability to humans is unresolved; preclinical endpoint, not clinical evidence of treatment efficacy or safety.

Limitations and uncertainties: Not a human study; no recommendation for oncological use. No uniform aromatase-inhibitor class effect.

Original sources for this finding: Cannabinol improves exemestane efficacy in estrogen receptor-positive breast cancer models: a comparative study with cannabidiol. [VF_P_40345424]

References and access status

[VF_L_D0396] FEMARA (LETROZOLE) TABLET, FILM COATED [NOVARTIS PHARMACEUTICALS CORPORATION]

Original source / bibliographic reference

Authors: Marketing authorisation holder; official product information via DailyMed

Year: 2026

Source type: Official medicine information; relevant identity, PK, PD and DDI sections read individually

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

Bibliographic attribution or source identity cross-checked.

[VF_P_37173983] Cannabidiol as a Promising Adjuvant Therapy for Estrogen Receptor-Positive Breast Tumors: Unveiling Its Benefits with Aromatase Inhibitors.

Original source / bibliographic reference

Authors: Almeida CF, Teixeira N, Valente MJ, Vinggaard AM, Correia-da-Silva G, Amaral C.

Year: 2023

Source type: Scientific publication; precise study type and suitability described in the finding or individual review

DOI: 10.3390/cancers15092517

PMID: 37173983

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

Bibliographic attribution or source identity cross-checked.

DOI – publisher access (access restrictions may apply)

[VF_P_40345424] Cannabinol improves exemestane efficacy in estrogen receptor-positive breast cancer models: a comparative study with cannabidiol.

Original source / bibliographic reference

Authors: Almeida CF, Valente MJ, Teixeira N, Rocha S, Ribeiro AP, Vinggaard AM, Correia-da-Silva G, Amaral C.

Year: 2025

Source type: Scientific publication; precise study type and suitability described in the finding or individual review

DOI: 10.1016/j.ejphar.2025.177712

PMID: 40345424

Source access – 23 October 2026: Direct retrieval could not be fully verified; availability remains unresolved.

Bibliographic attribution or source identity cross-checked.

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