Levothyroxine added to a low-calorie diet for adults with obesity and high‑normal or mildly elevated TSH

Is this trial a fit for you?

A plain-English reading of the study's rules. Only the study team can confirm whether you qualify.

What this trial studies

This is a phase III, randomized, double‑blind, placebo‑controlled multicentre trial in Spain enrolling 286 adults aged 25–60 with BMI 30.0–39.9 kg/m² who either have subclinical hypothyroidism (TSH 5–10 mIU/L with normal peripheral hormones) or are euthyroid with TSH in the upper reference tertile. Participants are randomized 1:1, stratified by age, sex, and BMI, to receive levothyroxine 88 µg once daily or placebo alongside a hypocaloric diet. The trial is conducted at multiple hospitals in Andalusia and will follow participants to measure weight change and related metabolic outcomes. Standard safety monitoring will be performed to detect thyroid hormone–related effects.

Why it matters

Who can join: the full rules

Inclusion Criteria:

* Adults 25-60 years of age.
* Obesity grade I-II: BMI 30.0-39.9 kg/m².
* Either subclinical hypothyroidism (TSH 5-10 mIU/L with normal peripheral hormones) or euthyroid with TSH in the highest tertile of the population reference range (no known thyroid disease).
* Able and willing to provide written informed consent.
* Women of childbearing potential: not pregnant or breastfeeding and using a highly effective contraception method (failure rate \<1%) per CTCG guidance (e.g., hormonal methods, IUD/IUS, sterilization, or dual barrier with spermicide).

Exclusion Criteria:

* Diabetes mellitus (HbA1c ≥6.5%, fasting glucose ≥126 mg/dL, or 2-h OGTT ≥200 mg/dL).
* Any prior thyroid disease (hyperthyroidism, overt hypothyroidism) or prior LT4 treatment.
* Current or recent (≤3 months) use of levothyroxine, hypoglycaemic agents, antibiotics, or regular probiotics/prebiotics.
* Active cancer or cancer within the last 5 years (except basal-cell carcinoma).
* Chronic liver disease with total bilirubin ≥2.0 mg/dL or AST \>3× ULN.
* Established cardiovascular disease (e.g., stroke, ischemic heart disease, peripheral artery disease).
* Atrial fibrillation or any arrhythmia history.
* Uncontrolled hypertension (\>160/100 mmHg) despite therapy (assessed by ABPM at screening).
* Any heart failure; resting HR \>85 bpm; eGFR \<60 mL/min.
* Known HIV, HBV, or HCV infection.
* Acute inflammatory disease or inflammatory bowel disease.
* Serious underlying disease that, in the investigator's judgment, could affect participation.
* Drug/alcohol abuse, life expectancy \<12 months, inability to follow the recommended diet or attend visits.
* Positive pregnancy test, pregnant, expecting pregnancy, or breastfeeding.
* Hypersensitivity to any component of the investigational product.
* Inability or unwillingness to provide informed consent.

Where it's running

• Hospital Universitario Virgen de la Victoria
  Málaga, Spain Recruiting
• Hospital Puerta del Mar
  Cadiz, Spain Not yet recruiting
• Hospital Reina Sofía
  Córdoba, Spain Not yet recruiting
• Hospital Universitario de Jaén
  Jaén, Spain Not yet recruiting
• Hospital Clínico Universitario de Valladolid
  Valladolid, Spain Not yet recruiting

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How to take part

1. Review the eligibility criteria above with your treating physician.
2. Check the official listing on ClinicalTrials.gov for the latest contact details and recruitment status.
3. Contact the study coordinator or principal investigator to ask for pre-screening. Pre-screening is free and never obligates you to enroll.