Levothyroxine (T4) vs Testosterone Cypionate

Mechanism

Synthetic thyroxine used to replace or augment thyroid hormone in hypothyroid states.

Contraindications

• Requires endocrine supervision and lab monitoring

Mechanism

Testosterone cypionate is an esterified prodrug of testosterone that undergoes hydrolysis in vivo to release free testosterone. It binds the androgen receptor (AR), activating genomic pathways via AR nuclear translocation and transcription of anabolic genes including IGF-1, satellite cell proliferation, and nitrogen retention. Additionally, testosterone exerts non-genomic effects through membrane-associated AR signaling, modulating calcium influx and MAPK/ERK pathways. Aromatization to estradiol via CYP19A1 (aromatase) maintains bone density and lipid profiles.

Standard Dosing

Research indicates 100-200 mg administered via intramuscular or subcutaneous injection every 7-14 days for testosterone replacement therapy.

Timing

Inject on a consistent schedule. Twice-weekly dosing (e.g., Monday/Thursday) reduces peak-trough fluctuations. Morning injection preferred for alignment with circadian testosterone rhythm.

Cycle Duration

Ongoing for TRT. If discontinuing, taper and implement PCT protocol. Testicular function suppression occurs within 2-4 weeks of initiation.

Side Effects

• Polycythemia / elevated hematocrit
• Acne and oily skin
• Testicular atrophy (without hCG)
• Gynecomastia (from aromatization)
• Mood changes and irritability
• Fluid retention
• Elevated liver enzymes (rare with injectable)
• Sleep apnea exacerbation

Contraindications

• Prostate cancer or elevated PSA without urological clearance
• Male breast cancer
• Polycythemia (hematocrit >54%)
• Untreated severe obstructive sleep apnea
• Uncontrolled heart failure
• Desire for near-term fertility (without hCG adjunct)
• Women who are pregnant or may become pregnant

Best Stacking Partners