Description
T3 is short for triiodothyronine, one of the body’s primary thyroid hormones, and it plays a huge role in metabolism, energy, and fat regulation. It’s a legitimate medical drug, but also (controversially) used in fitness and bodybuilding for fat loss.
⚗️ What T3 Is
| Category | Description |
| Chemical name | 3,3′,5-triiodo-L-thyronine |
| Common brand names | Cytomel, Liothyronine sodium |
| Hormone type | Thyroid hormone (metabolic regulator) |
| Produced naturally by | Thyroid gland (and converted from T4 – thyroxine) |
| Molecular formula | C₁₅H₁₂I₃NO₄ |
🧠 Biological Function
T3 regulates how fast your cells work — it’s the metabolic throttle of your body.
It increases:
- Basal metabolic rate (BMR)
- Body temperature
- Oxygen consumption
- Fat and carbohydrate metabolism
- Heart rate and alertness
When T3 is high → metabolism speeds up (more calories burned).
When low → metabolism slows down (fatigue, weight gain, cold intolerance).
💊 Medical Use (Normal Life)
T3 is prescribed medically for:
- Hypothyroidism (underactive thyroid)
- Myxedema coma (severe thyroid deficiency)
- Certain cases of depression (adjunct therapy)
- Sometimes as a diagnostic test for thyroid function
Typical therapeutic dose:
→ 25–75 mcg per day, adjusted by a doctor based on blood tests.
🏋️ Application in Fitness & Bodybuilding
T3 is not anabolic — it doesn’t build muscle.
But it’s very effective for fat loss, which is why it’s sometimes used (illegally) by athletes and bodybuilders, especially in cutting phases or pre-contest prep.
🔥 Intended (illicit) use
- Accelerates fat burning by raising metabolic rate
- Enhances nutrient turnover
- Increases energy and body heat (thermogenesis)
- Often combined with anabolic steroids to prevent muscle loss
⚙️ Typical (unofficial) “cycles”
⚠️ These are not medical recommendations, only descriptions of common misuse patterns.
| Phase | Dose | Duration |
| Start | 12.5–25 mcg/day | 3–4 days |
| Ramp-up | 25 → 50 → 75 mcg/day | Over 1–2 weeks |
| Max | 75–100 mcg/day | Held for 1–2 weeks max |
| Taper down | Reverse the increase | To prevent thyroid shock |
Total cycle length: 4–8 weeks, followed by a rest period for thyroid recovery.
⚠️ Risks and Side Effects
Because T3 affects every cell in the body, misuse can cause serious health problems.
Common side effects
- Rapid heartbeat (tachycardia)
- Nervousness, anxiety, tremors
- Sweating, heat intolerance
- Insomnia
- Muscle loss (catabolism)
- Fatigue or “crash” after stopping
Serious risks
- Permanent thyroid suppression (body stops producing its own T3)
- Arrhythmias / heart enlargement
- Bone density loss
- Metabolic rebound (rapid fat gain after stopping)
- Extreme muscle wasting if diet or anabolics don’t compensate
🧬 Legal and Doping Status
- Prescription-only drug in most countries.
- Banned by WADA as a hormone and metabolic modulator (S4 category).
- Athletes caught using it without medical reason can be disqualified or suspended.
✅ Summary
| Aspect | T3 (Liothyronine) |
| Type | Thyroid hormone |
| Use in medicine | Treats hypothyroidism |
| Effect | Boosts metabolism, burns fat |
| Dose (medical) | 25–75 mcg/day |
| Use in fitness (illicit) | Cutting, fat loss |
| Cycle length | 4–8 weeks |
| Main risk | Thyroid damage, heart strain, muscle loss |
| Legal status | Prescription only / banned in sport |
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