Side-by-side comparison of mechanisms, dosing, interactions, and stacking potential.
| Testosterone Cypionate | Thyroid (Levothyroxine / Liothyronine T3/T4) | |
|---|---|---|
| Category | Hormones | Hormones |
| Standard Dose | Research indicates 100-200 mg administered via intramuscular or subcutaneous injection every 7-14 days for testosterone replacement therapy. | Research indicates Levothyroxine (T4): 25-200 mcg daily based on TSH and free T4 levels. Liothyronine (T3): 5-25 mcg daily, often split into 2-3 doses. Combination T4/T3 ratio typically 4:1 to 3:1 when using both. |
| 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. | Levothyroxine: Take on empty stomach, 30-60 minutes before breakfast or at bedtime (3+ hours after last meal). Separate from calcium, iron, and antacids by 4 hours. Liothyronine: Split into 2-3 daily doses due to short half-life (2.5 hours for T3 vs. 6-7 days for T4). |
| Cycle Duration | Ongoing for TRT. If discontinuing, taper and implement PCT protocol. Testicular function suppression occurs within 2-4 weeks of initiation. | Ongoing for diagnosed hypothyroidism. Optimization protocols may be shorter-term (3-6 months) with reassessment. |
| Evidence Level | strong_human | strong_human |
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.
Research indicates 100-200 mg administered via intramuscular or subcutaneous injection every 7-14 days for testosterone replacement therapy.
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.
Ongoing for TRT. If discontinuing, taper and implement PCT protocol. Testicular function suppression occurs within 2-4 weeks of initiation.
Levothyroxine (T4) is a prohormone converted to the active triiodothyronine (T3) by type 1 and type 2 deiodinase enzymes (DIO1/DIO2) in peripheral tissues. T3 binds nuclear thyroid hormone receptors (TRa and TRb), forming heterodimers with retinoid X receptors (RXR) that bind thyroid response elements (TREs) in DNA, directly modulating transcription of genes controlling basal metabolic rate, thermogenesis, mitochondrial biogenesis (via PGC-1a), cardiac output, and neuronal development. T3 also exerts rapid non-genomic effects on mitochondrial respiration, ion channels, and cell membrane transport.
Research indicates Levothyroxine (T4): 25-200 mcg daily based on TSH and free T4 levels. Liothyronine (T3): 5-25 mcg daily, often split into 2-3 doses. Combination T4/T3 ratio typically 4:1 to 3:1 when using both.
Levothyroxine: Take on empty stomach, 30-60 minutes before breakfast or at bedtime (3+ hours after last meal). Separate from calcium, iron, and antacids by 4 hours. Liothyronine: Split into 2-3 daily doses due to short half-life (2.5 hours for T3 vs. 6-7 days for T4).
Ongoing for diagnosed hypothyroidism. Optimization protocols may be shorter-term (3-6 months) with reassessment.
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