Medical Oncologist
Abiraterone (Zytiga)
How Does Abiraterone Work? — The CYP17 Inhibitor Explained
Abiraterone blocks an enzyme that prostate cancer cells rely on to make testosterone. Understanding how it works — and why you take it with a steroid — helps you take it correctly and know what to watch for.
Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed August 2026
- Blocks the fuel supply — Prostate cancer cells use testosterone to grow. Abiraterone cuts off the enzyme that makes that testosterone.
- Works in three places at once — It acts on the adrenal glands, the testes, and inside the tumour itself — not just in one location.
- The steroid is not optional — Prednisone or prednisolone is prescribed alongside abiraterone for a specific physiological reason, not as an afterthought.
- Empty stomach is a safety rule — Taking abiraterone with food changes how much of it your body absorbs and raises the risk of side effects.
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Abiraterone blocks an enzyme called CYP17A1 that prostate cancer cells use to make testosterone. Without testosterone, prostate cancer has less fuel to grow. It works in the adrenal glands, the testes, and inside the tumour itself — cutting off androgen production more completely than standard hormone injections alone.
What is abiraterone actually doing inside your body?
Prostate cancer cells need testosterone and related hormones — called androgens — to grow. An enzyme called CYP17A1 is the key step in making those androgens, and it works inside your adrenal glands, your testes, and inside the tumour cells themselves.
Abiraterone is shaped to fit tightly into CYP17A1 and block it. When the enzyme is blocked, the assembly line that produces androgens stops, and prostate cancer cells are left without the hormones they depend on to divide.
This is why abiraterone is more thorough than older hormone therapies. Standard androgen deprivation injections stop the testes from producing testosterone, but they do not stop the adrenal glands or the tumour from making their own supply. Abiraterone addresses all three sources.
What to know before your first dose
- Take it on an empty stomachFood — especially fatty food — significantly increases the amount absorbed and raises the risk of side effects. Your package leaflet and pharmacist will confirm the window to observe before and after each dose.
- Always take it with the prescribed steroidYour oncologist will prescribe prednisone or prednisolone alongside abiraterone. The two are taken together every day, not separately or on alternate days.
- Never stop the steroid suddenlyIf you run out or feel you want to stop, call your team first. Stopping abruptly can cause a serious fall in cortisol that needs urgent attention.
- Monitor your blood pressure at homeAbiraterone can raise blood pressure. Your team will ask you to check it regularly and report readings that are higher than your usual baseline.
- Share every medication you takeAbiraterone interacts with a number of common medicines, including some blood thinners and heart drugs. Your pharmacist and oncologist need a complete, current list.
- Include supplements and herbal medicines in that listSeveral commonly used supplements can affect how abiraterone works. Your team cannot account for interactions they do not know about.
How abiraterone works — step by step
You swallow the tablet
Abiraterone acetate is the form in the tablet. Your gut converts it into its active form, abiraterone, which is then absorbed into your bloodstream.
The drug reaches where androgens are made
The bloodstream carries abiraterone to the adrenal glands above your kidneys, and to the prostate tumour and any cancer that has spread elsewhere in the body.
It binds to and blocks CYP17A1
CYP17A1 catalyses an essential early step in androgen production. Abiraterone fits into the enzyme's active site and occupies it, preventing the reaction from proceeding.
Androgen production stops
Without a functioning CYP17A1, the biochemical steps that produce testosterone and related hormones cannot continue. Androgen levels throughout the body fall significantly.
Prostate cancer cells lose their fuel
Prostate cancer cells depend on androgens to activate the androgen receptor, which drives cell growth. Without androgens, that signalling pathway is suppressed.
The steroid replaces what was disrupted
Blocking CYP17A1 also disrupts how the body makes cortisol. Prednisone or prednisolone is taken daily to replace that cortisol and prevent a build-up of other hormones that would cause side effects.
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MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
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Why is a steroid part of the prescription?
When abiraterone blocks CYP17A1, it also disrupts the pathway your body uses to make cortisol. Your body responds by releasing more of a signalling hormone — ACTH — trying to push the blocked pathway harder. That push causes a build-up of other hormones that act on your kidneys and can raise blood pressure, lower potassium, and cause fluid retention in your legs.
Prednisone or prednisolone is prescribed daily to replace the cortisol and suppress the ACTH response. This prevents those effects without interfering with how abiraterone works on the tumour.
The steroid is doing a specific physiological job — not simply reducing inflammation. If you cannot take it for any reason, tell your oncologist before you stop. There are alternatives, but the decision needs to be made with your team.
Questions people ask after abiraterone is prescribed
Will abiraterone cure my prostate cancer?
Abiraterone is not intended to cure prostate cancer. It is designed to control it — to slow growth, reduce PSA, and in a proportion of patients shrink the disease — for as long as it remains effective. For many men, that period of control is meaningful. ASCO and ESMO guidance describes the treatment as extending disease control in metastatic and high-risk settings, and your oncologist can explain what the aim is specifically for your situation.
What does 'castration-resistant' mean if this is a hormone treatment?
When a cancer is called castration-resistant, it means it continued to grow even after testosterone from the testes was removed by surgery or hormone injections. This was once thought to mean the cancer had become fully independent of androgens. Research later showed that these tumours often maintain androgen production through the adrenal glands and through their own internal enzyme activity. Abiraterone was developed to cut off those additional sources, which is why it can remain effective even after standard hormone therapy stops working.
Can the cancer become resistant to abiraterone over time?
Yes. In a proportion of patients, over time, prostate cancer finds ways around the block abiraterone creates. Mechanisms include changes to the androgen receptor that make it less dependent on androgens, and alternative pathways that bypass CYP17A1 entirely. This is why your oncologist monitors PSA and imaging at regular intervals — a rising PSA after a stable period is typically the first signal that the cancer is adapting. There are treatment options to consider when that happens, and your oncologist will discuss those when the time comes.
Is it safe to take alongside the hormone injection I am already on?
Yes. Abiraterone is typically given together with ongoing androgen deprivation therapy — the hormone injection — not instead of it. The injection suppresses testicular androgen production, and abiraterone addresses the remaining sources. Stopping the injection is not recommended without your oncologist's guidance. The two treatments work on different parts of the same pathway and are intended to be complementary.
Why does it matter so much that I take it on an empty stomach?
Food — especially high-fat food — markedly increases the amount of abiraterone absorbed from a single tablet. Regulatory submissions showed that taking it with food produced exposure in the blood many times higher than the fasted state. The dose your oncologist has prescribed is calculated for the fasted state. Taking it with food means receiving a much higher dose than intended, which raises the risk of side effects without improving the effect on the tumour. This is a pharmacokinetic constraint, not a general lifestyle suggestion — follow your package leaflet's specific instruction carefully.
What happens when abiraterone stops working?
Your oncologist will discuss the next option when that point comes. There are other treatments used after abiraterone, and the right choice at that stage depends on your general health, what your cancer looks like at the time, and what has been tried before. It is reasonable to ask your oncologist now what the landscape of your treatment plan looks like beyond abiraterone — knowing the broad path ahead can reduce anxiety, even if the details are filled in later.
Did you know?
Prostate cancer cells can manufacture their own testosterone even after the testes are surgically removed or chemically switched off. Research published in the New England Journal of Medicine showed that tumours maintain an internal androgen supply through their own enzyme activity — which is exactly what CYP17A1 enables.
This discovery was what led researchers to identify CYP17A1 as a therapeutic target and ultimately to develop abiraterone. Its approval by regulatory bodies including the US FDA and the European Medicines Agency changed the standard of care for advanced prostate cancer.
Source: de Bono JS et al., New England Journal of Medicine 2011; ESMO Clinical Practice Guidelines for Prostate Cancer
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Common questions
Frequently asked questions
How long does it take for abiraterone to start working?
Your oncologist will typically check your PSA within the first weeks to months to see whether it is falling. A falling PSA is usually the first measurable sign that the treatment is having an effect. Imaging is used at later intervals to assess whether the disease has responded in terms of size or spread. There is no single timeline — response varies from person to person — and your team will tell you what they are watching for and when.
What side effects should I report to my team straight away?
Contact your team the same day if you notice swelling in your legs or ankles that is new, a significant rise in your home blood pressure readings, muscle weakness, chest pain or breathlessness, or yellowing of the skin or eyes. These can be signs of the hormonal effects on the kidneys or of liver changes that need prompt assessment. Mild fatigue and minor fluid retention are common and manageable, but the symptoms above need same-day contact rather than waiting for your next scheduled visit.
Can I drink water before taking abiraterone?
Yes. Water is fine at any time. The restriction is on food — particularly fatty food — because food changes how much of the drug is absorbed. Plain water does not affect absorption. If you take other morning medications that need to be taken with food, speak with your pharmacist about how to space them so that abiraterone is taken appropriately away from your meal.
Will abiraterone affect my heart?
Abiraterone can cause fluid retention and raise blood pressure, both of which place additional load on the heart. Your oncologist will monitor your blood pressure, potassium levels, and liver function at regular intervals through blood tests. If you have existing heart disease or high blood pressure, make sure your cardiologist and oncologist are aware of your full medication list. Report any new breathlessness, ankle swelling, or irregular heartbeat to your team promptly rather than waiting.
Is abiraterone available at CION?
Abiraterone is an oral tablet taken at home, not an infusion given in a clinic. CION centres support you with treatment monitoring, managing side effects, and coordinating the blood tests and imaging your oncologist uses to assess response. PET-CT scans used in response assessment are coordinated through partner imaging centres. Speak to your oncologist about where prescriptions and monitoring will be managed in your specific case.
What should I tell my family about this drug?
Three things are most useful for them to know. First, the steroid tablet is as important as the abiraterone tablet — it should never be skipped or stopped without calling the team. Second, the empty-stomach rule applies every day, not just sometimes. Third, swelling in the legs, high blood pressure readings, or yellowing of the eyes are the symptoms to report the same day, not at the next appointment. Having a family member familiar with these points means there is a second pair of eyes if you feel unwell.