In this episode of “The Psych Consult: Second Opinion,” endocrinologist Caroline Messer, MD, joined consultation-liaison psychiatrist Claire Brandon, MD, to discuss where thyroid disease and psychiatric illness overlap, and where clinicians most often go wrong. Reading the LabsMesser advised psychiatrists to rely on thyroid-stimulating hormone (TSH) alone in most cases, reserving free T4 and T3 for suspected central disease. Stress, heparin, and binding-protein abnormalities can all distort peripheral levels. She noted that SSRIs can lower free T4 by causing a mild central hypothyroidism. Symptoms are a poor guide on their own. Messer pointed to the Colorado Thyroid Disease Prevalence Study, which evaluated more than 25,000 health fair attendees, as evidence of how common hypothyroid-type complaints are in the general population. Age further complicates interpretation: TSH distribution shifts upward over the lifespan, and most older adults with TSH above 4.5 mIU/L fall within an age-appropriate range. Treating those values as disease, she said, risks mislabeling depression in older adults as hypothyroidism. Wellness TrendsPatients increasingly arrive taking thyroid-related supplements. Low-dose T3, around 5 mcg, is unlikely to cause harm if TSH remains unsuppressed, Messer said, though she noted meta-analyses have not supported T3 augmentation for refractory depression. Bovine thyroid products are harder to assess because their content is often unknown. Iodine-rich supplements such as kelp pose a less obvious risk. In patients with Hashimoto thyroiditis, high iodine exposure can produce a permanent shutdown of hormone production, while patients with TSH receptor antibodies may develop hyperthyroidism. Brandon emphasized taking a thorough supplement history in any patient with new anxiety or mood changes. Monitoring and Follow-UpFor patients starting lithium, Messer recommended a baseline TSH, a repeat at 1 month, and testing every 6 months thereafter, cautioning against more frequent checks. Both speakers agreed that serial testing driven by health anxiety offers only brief reassurance and may reinforce the cycle. When hypothyroidism is treated, symptom relief can trail TSH normalization by several months, so dose escalation is not automatically warranted. “We’re all colleagues and we can all just curbside each other,” said Messer.
