The Study
Interrelationships in the regulation of TSH and prolactin secretion in man: effects of L-dopa, TRH and thyroid hormone in various combinations.
This study just watched what happened to 13 people when they took some medicines, and saw tiny changes in their body chemicals. But it didn’t compare them to anyone else or test anything fairly, so we can’t say the medicine caused the changes — it’s just a snapshot.
Analysis score
Maximum 58 for a case-control study.
Where the score came from
When people take thyroid hormone pills, their body stops responding as strongly to a signal (TRH) that normally tells the thyroid to make more hormone, but it still responds normally to signals that make prolactin.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 521 / 100
Quality score
Researchers compare people who have a condition (cases) with similar people who do not (controls), looking back in time for differences in exposure. Useful but more prone to bias.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Yes — this shows thyroid hormone replacement suppresses one feedback pathway (TSH) but not another (prolactin), which helps explain how hormone therapy stabilizes thyroid levels.
- 2In 13 people: L-dopa didn't change TSH; TRH didn't raise TSH during hormone replacement, but did raise prolactin normally.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
The Journal of clinical endocrinology and metabolism
Year
1974
Authors
S. Refetoff, V. Fang, B. Rapoport, H. Friesen
Related Content
Claims (3)
When thyroid hormone levels in the blood are high, the pituitary gland reduces production of thyroid-stimulating hormone. When thyroid-stimulating hormone levels are low, the thyroid gland produces thyroid hormones without normal regulatory control.
In people with normal thyroid function, taking L-dopa does not result in a detectable change in thyroid-stimulating hormone levels because any changes are too small to be measured by standard tests.
In people taking thyroid hormone medication who have normal thyroid function, the pituitary gland releases less TSH in response to TRH, but releases the same amount of prolactin as before, indicating that the two hormones are regulated differently during hormone replacement.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.