Medicines, foods and supplements to avoid on goserelin

Compared with many cancer medicines, goserelin (Zoladex) has relatively few interactions of the usual kind. It is a small protein-like molecule that is broken down differently from most tablets, so it is not strongly affected by the liver enzymes that cause many medicine clashes. That does not mean anything goes. The biggest issue is with products that work against its purpose. Goserelin lowers oestrogen to help control hormone receptor positive breast cancer, so hormone replacement therapy, the combined contraceptive pill and other oestrogen-containing products are usually avoided, and some herbal supplements marketed for menopause may contain plant oestrogens. A second point is heart rhythm. Medicines that lower sex hormones can occasionally lengthen a measure of heart rhythm called the QT interval, so doctors take care when combining goserelin with other medicines that do the same. Third, because the implant goes under the skin of the belly, blood thinners can make bruising or bleeding at the implant site more likely. Finally, many of the most important interactions come from the medicines given alongside goserelin, such as tamoxifen, aromatase inhibitors or CDK4/6 inhibitors, each of which has its own list. There are no specific foods to avoid because of goserelin itself. The safest habit is to tell every doctor, dentist and pharmacist that you are on goserelin, and to check before starting anything new.

Avoid adding oestrogen

Hormone-containing medicines and some menopause supplements can undo what goserelin is doing.

Take care with heart rhythm medicines

Your doctor will check if you take other medicines that affect the QT interval.

Remember the partner medicines

Tamoxifen and CDK4/6 inhibitors often have more interactions than goserelin itself.

Interaction advice is partly based on firm evidence and partly on caution.

Formal studies are limited

Few dedicated studies have tested goserelin with other medicines, so some advice is based on how it works.

Herbal products are hard to judge

Supplements vary in content and strength, and many have never been tested with cancer medicines.

Diet soy is different from supplements

Normal amounts of soy foods such as tofu or soy milk are generally considered safe. Concentrated supplements are the concern.

What this page cannot tell you

It cannot check your own list of medicines. A pharmacist or your oncologist can review everything you take together.

A few habits help avoid problems when several doctors are involved.

Keep one list

Carry an up-to-date list of every medicine, supplement and remedy, with doses, on paper or your phone.

Mention cancer treatment every time

Tell your dentist, family doctor and pharmacist that you are on goserelin and any partner medicines.

Ask one question

Before starting anything new, ask whether it is safe with your hormone treatment for breast cancer.