T4 (Levothyroxine/Synthroid) — Dosing, Cycles, Half-Life & Side Effects
T4 (Levothyroxine/Synthroid) is a thyroid hormone with a half-life of 7 days. Thyroid prohormone that converts to T3, milder and longer-acting than direct T3. This page is educational harm-reduction reference compiled from peer-reviewed literature — not medical advice, not an endorsement, not a recommendation to use. Consult a licensed clinician before any decision.
Quick Facts
| Class | Thyroid Hormone |
|---|---|
| Half-life | 7 days |
| Hepatotoxicity | None |
| Suppression | 0/10 |
Typical Dosing Ranges
Common dose range: 50-200mcg/day
Cycle length: 4-12 weeks with taper
Dose ranges are compiled from published pharmacokinetic studies and community-reported usage. Where a value is community-reported rather than clinically studied, this page and its structured data flag it. Lower end of any range is always the safer starting point.
Stacking Considerations
- No structural stacking blockers. Standard harm-reduction rules apply: minimize total androgen load, minimize oral exposure, and monitor bloodwork.
PCT Requirements
- Never stack two SERMs. Extend a single SERM (tamoxifen OR enclomiphene/clomiphene) rather than combining.
- Use the cycle planner to generate a full protocol based on your complete stack, not this compound alone.
Side Effect Profile
- Slower acting
- Requires conversion to T3
- Thyroid suppression
- Weaker effects
Known Interactions
No compound-specific interactions are catalogued in the current matrix. This does not mean no risk exists — it means there is no curated pairwise entry.
Related compounds
T3 (Cytomel/Liothyronine)
Thyroid Hormone · t½ 24 hours
Albuterol
Beta-2 Agonist · t½ 4-6 hours
Clenbuterol
Beta-2 Agonist · t½ ~35 hours in healthy adult humans (Yamamoto et al. 1985, J Pharmacobiodyn, PMID: 4045696, oral 20-80 mcg). Earlier 36-48h estimates appear to have conflated with non-human data (rabbits ~9h, rats ~30h in the same study).
DNP (2,4-Dinitrophenol)
Mitochondrial Uncoupler · t½ 36 hours
Monitoring (Bloodwork & Vitals)
- Comprehensive metabolic panel (baseline, mid-cycle, post-cycle)
- Lipid panel (total cholesterol, HDL, LDL, triglycerides)
- CBC (hemoglobin, hematocrit — watch for erythrocytosis)
- Sex-hormone panel (Total T, Free T, Estradiol sensitive, SHBG, LH, FSH)
- Blood pressure (weekly self-check; flag systolic >140 or diastolic >90)
Baseline bloodwork is recommended before any cycle. Discontinue if liver enzymes exceed 3× upper limit of normal or if hematocrit exceeds 54%.
Frequently Asked Questions
What is the half-life of T4 (Levothyroxine/Synthroid)?
T4 (Levothyroxine/Synthroid) has a half-life of approximately 7 days. This figure is used to determine injection frequency (for esters) and post-cycle clearance timing.
What is the typical dose range for T4 (Levothyroxine/Synthroid)?
Commonly reported ranges for T4 (Levothyroxine/Synthroid): 50-200mcg/day. Cycle length: 4-12 weeks with taper. These are compiled from published studies and community-reported usage — individual response varies and lower end is always preferred.
Does T4 (Levothyroxine/Synthroid) suppress natural testosterone?
T4 (Levothyroxine/Synthroid) causes minimal suppression of the HPTA axis (score 0/10). PCT may still be advisable depending on stack and duration.
What is T4 (Levothyroxine/Synthroid) typically used for?
T4 (Levothyroxine/Synthroid) is commonly used for: Metabolic support, Thyroid replacement, Mild cutting. Intended-use context does not imply safety — every use case carries the same underlying pharmacological risks.
Is T4 (Levothyroxine/Synthroid) legal?
T4 (Levothyroxine/Synthroid) is a controlled substance in many jurisdictions (typically Schedule III in the US when it is an anabolic androgenic steroid). StackItSmart does not provide sourcing information. Possession, import, and use without a prescription carry legal consequences that vary by country and state.
Citations
Disclaimer
StackItSmart is an independent harm-reduction reference. The content above is compiled from peer-reviewed literature and is not medical advice, not an endorsement, and not a recommendation to use T4 (Levothyroxine/Synthroid). Performance-enhancing compounds carry legal, endocrine, cardiovascular, and hepatic risks. Consult a licensed clinician before any decision. StackItSmart does not provide sourcing, procurement, or dosing prescriptions.