Cannabis formulations reduced tamoxifen effectiveness against breast cancer cells in lab | Research

The takeaway

In breast cancer cell lines, combining cannabinoids with tamoxifen diminished the drug's anti-proliferative activity, especially with recreational-type cannabis ratios.

Breast cancer patients using cannabis, oncologists, and researchers studying drug interactions with cannabinoids.

Recreational cannabis formulations most reduced tamoxifen effectiveness

What the researchers found

Simultaneous treatment of MCF-7 breast cancer cells with various cannabinoid formulations and tamoxifen resulted in diminished anti-proliferative activity of tamoxifen, with the effect more pronounced with recreational cannabis formulations (higher THC).

Why it matters

Many cancer patients use cannabis for symptom management during treatment. If cannabinoids interfere with tamoxifen effectiveness, this could have real clinical consequences for breast cancer outcomes.

The numbers in context

An intra-entourage effect was found in MCF-7 cells with recreational but not medicinal cannabis formulations. No inter-entourage effects in either cell line. Tamoxifen's anti-proliferative activity was diminished when combined with cannabinoids, especially recreational formulations.

How the study worked

In vitro study using two breast cancer cell lines (MCF-7 and MDA-MB-231). Tested purified phytocannabinoid combinations mimicking medicinal and recreational cannabis strains, a Cannabis sativa extract, and combinations with tamoxifen.

What this study cannot tell us

This is a cell-line study, and in vitro results may not reflect what happens in the human body. Only two cell lines were tested. The cannabinoid concentrations used may not match those achieved in human tissue.

How to read the evidence

Preliminary: in vitro cell-line study only, no human or animal data.

When this study was published

Published in 2022.

The bigger picture

This is one of the first studies to directly test whether cannabis formulations interfere with a commonly prescribed breast cancer drug. The results raise a cautionary flag for the growing number of cancer patients using cannabis alongside conventional treatment.

Questions still open

Does this tamoxifen interference occur at cannabinoid concentrations achievable in human breast tissue? Would the same interference apply to other hormonal breast cancer treatments? Should cancer patients be advised about timing of cannabis use relative to tamoxifen doses?

Common questions

How did cannabis affect tamoxifen?

When cannabinoid formulations were applied simultaneously with tamoxifen to breast cancer cells, tamoxifen was less effective at stopping cancer cell growth. The interference was greater with high-THC recreational formulations.

Why might THC interfere with tamoxifen specifically?

The researchers found THC may partially exert its effects through the estrogen receptor, which is the same receptor tamoxifen targets in ER-positive breast cancer cells (MCF-7).

Should breast cancer patients stop using cannabis?

This study alone cannot answer that question. It provides a laboratory signal that warrants further investigation, but human studies are needed to determine whether this interaction occurs in actual patients.

Read the original research

Cannabis with breast cancer treatment: propitious or pernicious?

3 Biotech, 12(2), 54

View on PubMed ↗Publisher’s paper ↗

Citation

Schoeman, Recardia; de la Harpe, Amy; Beukes, Natasha; Frost, Carminita L. (2022). Cannabis with breast cancer treatment: propitious or pernicious?. 3 Biotech, 12(2), 54. https://doi.org/10.1007/s13205-021-03102-1