Abarelix vs Degarelix
GnRH Antagonist for Advanced Prostate Cancer Treatment
Fast-acting GnRH antagonist that rapidly lowers testosterone for advanced prostate cancer treatment
Written by Michael Carroll — Owner, Director of Research · Reviewed by the Peptide Initiative Research Team · Editorial standards
Quick comparison
Dose range
Abarelix
100–100 mg
Degarelix
80–80 mg
Frequency
Abarelix
Once daily
Degarelix
Once daily
Administration
Abarelix
Intramuscular injection (depot formulation)
Degarelix
As directed by healthcare provider
Cycle length
Abarelix
Ongoing/indefinite
Degarelix
Ongoing/indefinite
Onset speed
Abarelix
Moderate (1-2 weeks)
Degarelix
Moderate (1-2 weeks)
Evidence level
Abarelix
Strong human trials (Phase 3 or FDA approved)
Degarelix
Strong human trials (Phase 3 or FDA approved)
Benefit ratings
Rapid Hormone Control
Advanced Cancer Management
Patient Tolerability
Rapid Testosterone Control
Extended Duration
Clinical Efficacy
Compound specifications
Abarelix
Molecular formula
C72H95ClN14O14
Molecular weight
1416.1 g/mol
Half-life
Approximately 13 days
Bioavailability
~100% (intramuscular depot injection)
CAS number
183552-38-7
Degarelix
Molecular formula
C82H103ClN18O16
Molecular weight
1632.3 Da
Half-life
~53 days (median terminal half-life)
Bioavailability
100% (subcutaneous injection)
CAS number
214766-78-6
Dosing compared
Abarelix
Intramuscular
100 mg
Day 1, 15, 29, then every 4 weeks · Up to 12 months (effectiveness beyond 12 months not established)
This is the FDA-approved dose for advanced prostate cancer. A 100 mg shot is given into the buttock muscle on day 1, 15, and 29, then once every 4 weeks. The drug was sold as Plenaxis. [4]
Degarelix
Subcutaneous
240 mg (two 120 mg injections)
One time (loading dose) · Single starting dose
FDA-approved loading dose for advanced prostate cancer, given as two separate deep injections under the skin of the belly. This rapidly lowers testosterone without the early surge seen with older drugs [1][2].
80 mg
Every 28 days · Ongoing
FDA-approved maintenance dose, started 28 days after the loading dose. Keeps testosterone at castrate levels in over 97% of patients [1][2].
Best suited for
Abarelix
Reducing testosterone levels in prostate cancer
Abarelix is particularly well-suited for individuals focused on reducing testosterone levels in prostate cancer. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Slowing cancer progression in advanced disease
Abarelix is particularly well-suited for individuals focused on slowing cancer progression in advanced disease. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Managing hormone-dependent cancer symptoms
Abarelix is particularly well-suited for individuals focused on managing hormone-dependent cancer symptoms. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Degarelix
Men with advanced or metastatic prostate cancer requiring rapid hormone control
Degarelix is particularly well-suited for individuals focused on men with advanced or metastatic prostate cancer requiring rapid hormone control. [1][2] Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Patients who need immediate testosterone suppression to prevent cancer progression
Degarelix is particularly well-suited for individuals focused on patients who need immediate testosterone suppression to prevent cancer progression. [1][2] Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Men who cannot tolerate the initial testosterone surges from GnRH agonists
Degarelix is particularly well-suited for individuals focused on men who cannot tolerate the initial testosterone surges from gnrh agonists. [5][6] Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Side effects
Abarelix
Common
- Mild discomfort at treatment site
- Hot flashes and sweating
- Decreased libido and sexual dysfunction
- Increased liver enzymes
- Injection site reactions (pain, redness, swelling)
- Abdominal pain and gastrointestinal symptoms
- Headache and dizziness
- Weight changes
- Gynecomastia (breast tissue enlargement)
- Bone density loss with long-term use
Serious
- Severe allergic reaction
Degarelix
Common
- Mild discomfort at treatment site
- Injection site pain (28% of patients)
- Injection site redness or erythema (17%)
- Hot flashes (26% experience them)
- Increased liver enzymes and gamma-glutamyltransferase (10%)
- Weight gain (9%)
- Hypertension or elevated blood pressure (6%)
- Back pain (6%)
- Chills (5%)
- Constipation (5%)
- Urinary tract infection (5%)
- Injection site swelling (6%)
- Injection site induration or hardness (4%)
- Decreased sex drive and erectile dysfunction
- Gynecomastia (breast tissue growth)
- Testicular atrophy (shrinking)
Serious
- Severe allergic reaction
Safety & evidence
Abarelix
Evidence level
Strong human trials (Phase 3 or FDA approved)
FDA status
FDA approved for other use
Safety overview
Abarelix carries significant safety concerns primarily related to histamine release reactions, which led to its voluntary withdrawal from the U.S. market in 2006. Serious allergic responses including anaphylaxis, flushing, and hypotension have been documented. Long-term use poses substantial risks of bone density loss, cardiovascular effects from hormonal suppression, and metabolic complications including weight gain and altered lipid profiles. Liver enzyme elevations occur in 5-10% of patients. All use requires intensive medical supervision with regular monitoring of testosterone levels, liver function, bone density, and cardiovascular markers.
Contraindications
- Pregnancy or lactation
- Severe hypersensitivity reactions to peptide therapeutics
- History of anaphylaxis with similar compounds
Degarelix
Evidence level
Strong human trials (Phase 3 or FDA approved)
FDA status
FDA approved for this use
Safety overview
Degarelix is an FDA-approved GnRH antagonist with safety data from Phase 3 trials and post-market use in prostate cancer treatment. [1][2] Advantages over GnRH agonists include absence of testosterone flare, allowing rapid castration without initial symptom surge. [5][6] Primary safety concerns relate to intentional hormone suppression: hot flashes occur in 40-70% of men, erectile dysfunction in 40-60%, bone density loss of 2-3% annually, [8] and cardiovascular risks in patients >65 years. [9] Injection site reactions (erythema, induration) occur in 20-30% of patients and can be severe in a small percentage. [2] Liver enzyme elevations appear in 5% of patients. [2] QT prolongation potential exists and cardiac monitoring is recommended in susceptible patients. [2]
Contraindications
- History of severe hypersensitivity to degarelix
- Allergy to any product components (mannitol or other additives)
- Active untreated severe anaphylaxis risk
Which is right for you?
Choose Abarelix if...
- Reducing testosterone levels in prostate cancer
- Slowing cancer progression in advanced disease
- Managing hormone-dependent cancer symptoms
Choose Degarelix if...
- Men with advanced or metastatic prostate cancer requiring rapid hormone control
- Patients who need immediate testosterone suppression to prevent cancer progression
- Men who cannot tolerate the initial testosterone surges from GnRH agonists