T4 (levothyroxine) is a thyroid hormone that regulates metabolism, energy production, and protein synthesis. While not approved or safe for bodybuilding purposes, some athletes and bodybuilders misuse it for perceived benefits. Below is an objective breakdown of its purported uses, risks, and considerations:

Purported Benefits
1. Increased Metabolic Rate:
– T4 raises basal metabolic rate (BMR), potentially accelerating fat loss during cutting phases.
– May help achieve a leaner physique by burning more calories at rest.

2. Enhanced Fat Loss:
– Combined with a calorie deficit, T4 *might* amplify fat oxidation, though this comes with significant risks.

3. Muscle Preservation (Debatable):
– In theory, T4 could help retain muscle mass during extreme calorie deficits by maintaining metabolic efficiency. However, excessive doses can lead to muscle catabolism (breakdown).

4. Energy & Endurance:
– Elevated thyroid hormone levels *might* improve energy and workout stamina, but this is often offset by side effects like jitteriness or fatigue.