Goserelin side effects: the complete list and timeline

Almost every side effect of goserelin, also known as Zoladex, comes from the same thing that makes it work: a sharp fall in oestrogen once the ovaries are switched off. In practice this means the effects look very like a sudden menopause. Hot flushes and sweats are the most common, and many women also notice vaginal dryness, lower interest in sex, changes in mood, poorer sleep, headaches and aching joints. Periods usually stop within the first couple of months, though some spotting or a final period is common early on. Over months and years, low oestrogen also thins the bones, which is why bone health is monitored. At the implant site, a bruise or soreness is common, and rarely there can be more serious bleeding. When goserelin is combined with an aromatase inhibitor, joint aches and bone loss tend to be more marked than with tamoxifen. Most side effects are manageable with practical steps, non-hormonal medicines and support, and they usually fade over the months after treatment stops. A few effects are uncommon but important, including allergic reactions, very low mood and, for people whose cancer has spread to bone, a short-lived flare of pain when treatment starts. Knowing the pattern helps you recognise what is expected and what needs a call to your team.

Most effects are menopause effects

Hot flushes, dryness, mood and sleep changes all trace back to low oestrogen.

Timing follows the hormones

Symptoms usually start within the first few weeks, as oestrogen falls, and often ease a little with time.

Most effects are reversible

After goserelin stops, most symptoms settle as the ovaries recover, although bone changes take longer.

For many women, the side effects of goserelin are the most difficult part of breast cancer treatment in the long run, because they carry on for years.

They can be strong

Because menopause arrives within weeks rather than over years, symptoms are often more intense than a natural menopause.

Hormone replacement is not usually an option

HRT would put back the oestrogen the treatment is removing, so non-hormonal approaches are used instead.

They affect people stopping treatment

Studies show that side effects are a common reason for stopping hormone treatment early. Raising problems early gives your team the chance to help before that point.

What this page cannot tell you

It cannot predict which side effects you will have or how strong they will be. It also cannot weigh them against the benefit for you. Your oncologist can help you think that through.

Bone thinning causes no symptoms until a bone breaks, so it is checked rather than waited for.

Scans

A bone density scan is usually advised at the start, especially with an aromatase inhibitor, and repeated at intervals your team decides.

Everyday steps

Weight-bearing exercise such as brisk walking, muscle-strengthening work, enough calcium and vitamin D, not smoking and limiting alcohol all support bone strength.

Bone medicines

If bone density is low or falling, medicines such as zoledronic acid or denosumab may be offered.