Fertirelin vs Human Chorionic Gonadotropin (HCG)
A potent GnRH analog designed to support reproductive function in veterinary and research settings
A powerful hormone that mimics luteinizing hormone (LH) to stimulate your body's natural testosterone production while keeping your fertility intact—like having your cake and eating it too for men on hormone therapy.
Written by Michael Carroll — Owner, Director of Research · Reviewed by the Peptide Initiative Research Team · Editorial standards
Quick comparison
Dose range
Fertirelin
50–100 mcg
Human Chorionic Gonadotropin (HCG)
500–1500 IU
Frequency
Fertirelin
Once daily
Human Chorionic Gonadotropin (HCG)
Twice weekly
Administration
Fertirelin
Intramuscular injection
Human Chorionic Gonadotropin (HCG)
Subcutaneous injection
Cycle length
Fertirelin
Ongoing/indefinite
Human Chorionic Gonadotropin (HCG)
Ongoing/indefinite
Onset speed
Fertirelin
Moderate (1-2 weeks)
Human Chorionic Gonadotropin (HCG)
Moderate (1-2 weeks)
Evidence level
Fertirelin
Moderate human trials (Phase 1-2)
Human Chorionic Gonadotropin (HCG)
Strong human trials (Phase 3 or FDA approved)
Benefit ratings
Reproductive Synchronization
Hormone Support
Veterinary Breeding Enhancement
Fertility Preservation
Testicular Health
Hormone Balance
Compound specifications
Fertirelin
Molecular formula
C55H76N16O12
Molecular weight
1153.3 g/mol
Half-life
Variable depending on formulation; sustained-release formulations extend duration
Bioavailability
High when administered via injection
CAS number
66002-66-2
Human Chorionic Gonadotropin (HCG)
Molecular formula
C1105H1770N318O336S26 (approximate)
Molecular weight
36,700 g/mol (approximately)
Half-life
24-36 hours
Bioavailability
High when injected subcutaneously or intramuscularly
CAS number
9002-61-3
Dosing compared
Fertirelin
Intramuscular
50-100 mcg per animal
Single injection at the defined point in the synchronization protocol · Single dose (repeated per breeding cycle as needed)
Fertirelin is a veterinary GnRH agonist. In dairy cattle, 50 mcg and 100 mcg intramuscular both triggered an LH surge and comparable conception rates for ovulation synchronization and fixed-time insemination [4]. Used to induce ovulation and improve conception in cattle [1].
Human Chorionic Gonadotropin (HCG)
Subcutaneous
500-1,500 IU
2-3 times per week · Ongoing with TRT
Documented clinical practice for preserving testicular function/fertility in men on testosterone therapy; 1,500-2,000 IU 2-3x/week is used for hypogonadotropic hypogonadism [6]. The popular 500 IU 2-3x/week maintenance figure reflects real-world practice rather than the FDA label. In controlled dosing, 250 IU every other day held intratesticular testosterone within 7% of baseline and 500 IU raised it 26% above baseline during testosterone administration [7]; 500 IU every other day preserved semen parameters with no azoospermia in men on TRT [8].
Intramuscular
500-1,000 IU
3 times weekly for 3 weeks, then 2 times weekly for 3 weeks · 6-week induction course
FDA-labeled regimen for male hypogonadotropic hypogonadism (Pregnyl) [7]. Intramuscular is the only labeled route.
4,000 IU then taper to 2,000 IU
3 times weekly · 4,000 IU for 6-9 months, then 2,000 IU for 3 additional months
Higher-dose FDA-labeled regimen for inducing spermatogenesis/testicular descent (Pregnyl) [7].
Best suited for
Fertirelin
Livestock breeding programs
Fertirelin is particularly well-suited for individuals focused on livestock breeding programs. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Reproductive synchronization in cattle
Fertirelin is particularly well-suited for individuals focused on reproductive synchronization in cattle. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Fertility enhancement in veterinary settings
Fertirelin is particularly well-suited for individuals focused on fertility enhancement in veterinary settings. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Research on reproductive hormone mechanisms
Fertirelin is particularly well-suited for individuals focused on research on reproductive hormone mechanisms. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Human Chorionic Gonadotropin (HCG)
Fertility Preservation During TRT
If you're on testosterone therapy but want to keep your swimmers swimming, HCG is your best friend. It keeps your testes active and producing sperm even when external testosterone would normally shut that down. Research shows it can maintain or restore spermatogenesis in about 80% of men [3][4][8].
Preventing Testicular Atrophy
Nobody wants their boys to shrink. When you take external testosterone, your brain stops signaling your testes to work—and they get smaller from disuse. HCG mimics the signal (LH) that keeps them active, maintaining their size and function [6][14].
Hypogonadotropic Hypogonadism
If your pituitary gland isn't sending the right signals to your testes (low LH), HCG can step in and do the job. It's been used for decades to treat this condition, helping men achieve normal testosterone levels and fertility [3][6][13].
Post-Cycle Therapy (PCT)
After using anabolic steroids, your natural hormone production is suppressed. HCG can help jumpstart your testes back into action, speeding up the recovery of your natural testosterone production. It's often used as part of a comprehensive PCT protocol [9][15].
Side effects
Fertirelin
Common
- Mild discomfort at treatment site
- Transient hormone fluctuations
- Temporary behavioral changes in animals
- Mild injection site reactions
- Short-term changes in appetite
- Temporary mood variations
- Minimal systemic effects at therapeutic doses
Uncommon
- Occasional swelling at injection site
Serious
- Severe allergic reaction
Human Chorionic Gonadotropin (HCG)
Common
- Injection site reactions
- Headache
- Water retention
Uncommon
- Gynecomastia
- Mood changes
- Acne
Serious
- Blood clots
Safety & evidence
Fertirelin
Evidence level
Moderate human trials (Phase 1-2)
FDA status
Research compound
Safety overview
Fertirelin is a GnRH agonist developed specifically for veterinary use in livestock, particularly cattle breeding and fertility management. The peptide has been safely used in veterinary medicine for over 40 years with a well-documented safety profile in animals. Important limitation: Fertirelin is NOT approved for human use. All safety and efficacy data comes from veterinary applications in cattle and limited laboratory research. Human safety data is minimal and extrapolation from veterinary use is problematic. The biphasic response (initial hormone surge followed by suppression) must be carefully managed in any application. Individual responses can vary significantly based on age, hormonal status, and concurrent medications.
Contraindications
- Pregnancy (may disrupt existing pregnancy)
- Hypersensitivity to GnRH analogs
- Active reproductive infections
- Concurrent use with certain medications
- Undiagnosed reproductive disorders
Human Chorionic Gonadotropin (HCG)
Evidence level
Strong human trials (Phase 3 or FDA approved)
FDA status
FDA approved for other use
Safety overview
HCG has been used medically for over 80 years with a well-established safety profile. [10] When used appropriately for male hypogonadism or fertility preservation, side effects are generally mild and manageable. The most common issues relate to elevated estrogen from increased testosterone aromatization, which can be managed with aromatase inhibitors if needed. [6][18] Serious side effects are rare when HCG is used under medical supervision.
Contraindications
- Hormone-sensitive cancers (prostate, breast)
- Precocious puberty in children
- Known allergy to HCG or any component
- Pregnancy (in therapeutic male contexts)
- Untreated thyroid or adrenal disorders
Which is right for you?
Choose Fertirelin if...
- Livestock breeding programs
- Reproductive synchronization in cattle
- Fertility enhancement in veterinary settings
- Research on reproductive hormone mechanisms
Choose Human Chorionic Gonadotropin (HCG) if...
- Fertility preservation during TRT
- Maintaining testicular size and function
- Natural testosterone stimulation
- Post-cycle therapy recovery