Starting hormone therapy can feel overwhelming, especially when you are presented with different injection options and unfamiliar drug names.
The reassuring truth is that all of these treatments aim to do the same essential job. The differences are mostly about how quickly they work, how they are given, and what best fits your medical situation and daily life.
In simple terms
Hormone therapy lowers testosterone to slow prostate cancer growth.
Agonists and antagonists do this in slightly different ways — and in most cases, either can be appropriate.
What hormone therapy (ADT) does
Prostate cancer often relies on testosterone to grow. Androgen deprivation therapy (ADT) lowers testosterone to very low levels or blocks its effect. It is a foundation treatment and is often combined with other therapies.
Two main ways hormone therapy is given
GnRH agonists (often called “agonists”)
Agonists initially stimulate the pituitary gland, which can cause a temporary rise in testosterone before levels fall. This early rise is called a “flare.”
Because of this, some people are given a short course of another hormone-blocking tablet at the start, particularly if symptoms could worsen during this brief period.
GnRH antagonists (often called “antagonists”)
Antagonists block the signal immediately, so testosterone levels fall quickly without a flare.
They are often preferred when:
• rapid testosterone suppression is important
• avoiding flare matters
• early symptom control is needed
Common examples used in Australia
Agonists
Leuprorelin
Goserelin
Triptorelin
Antagonists
Degarelix (monthly injection)
Relugolix (daily tablet, where available and appropriate)
How they are given
Agonists are usually long-acting depot injections (often every 1–6 months).
Antagonists are given as a monthly injection or a daily tablet, depending on the drug.
Side effects
Because both classes lower testosterone, their side effects are largely similar. These may include hot flushes, fatigue, sexual changes, mood changes, loss of muscle, bone thinning over time, and metabolic changes. Many of these effects are manageable with monitoring and support.
So how do you choose?
In many situations, there is no single “right” answer. The choice depends on:
• whether a testosterone flare would be risky
• how quickly testosterone needs to fall
• convenience and access
• heart or metabolic health
• preference for injections versus tablets
Your oncology team considers all of these together, rather than focusing on the drug name alone.
Why this matters
Starting hormone therapy promptly is often more important than finding the “perfect” option. Both agonists and antagonists are effective, and treatment can be adjusted over time.
Key takeaway
Hormone therapy is the foundation of treatment.
Agonists and antagonists are usually equally effective.
In selected situations with extensive disease, an antagonist may be preferred for faster control.