Thyroid Modulator

An 8-week randomised, double-blind, placebo-controlled trial gave 600 mg a day of root extract to adults with subclinical hypothyroidism. It significantly lowered TSH and raised T3 and T4 toward normal against placebo ^{1Reference 1Sharma AK et al. · 2018RCTEfficacy and safety of ashwagandha root extract in subclinical hypothyroid patients — a double-blind, randomised placebo-controlled trialView study →}.

A substudy inside a placebo-controlled trial in people with bipolar disorder, who were not selected for thyroid disease, found subtle rises in the same thyroid indices ^{2Reference 2Gannon JM et al. · 2014RCTSubtle changes in thyroid indices during a placebo-controlled study of an extract of Withania somnifera in persons with bipolar disorderView study →}. The axis moved in the same direction in people with nothing to correct.

Case reports document ashwagandha precipitating thyrotoxicosis, with painless thyroiditis reported in the same setting ^{3Reference 3van der Hooft CS et al. · 2005Case reportThyrotoxicosis following the use of ashwagandha — case reportView study →}. Case reports are weak evidence for benefit and strong evidence that the pharmacology is real.

There is one small efficacy trial, no data at all in overt hypothyroidism, and the active constituent has not been identified — so no chemotype, extract ratio or withanolide content can be preferred.

In human thyroid plasma membranes, freeze-dried aqueous extracts of L. virginicus and L. europaeus produced dose-related, ultimately complete inhibition of TSH binding and of TSH-stimulated adenylate cyclase ^{4Reference 4Auf’mkolk et al. · 1984In vitroInhibition by certain plant extracts of the binding and adenylate cyclase stimulatory effect of bovine thyrotropin in human thyroid membranes — in vitroView study →}. A companion study showed the same extracts, and auto-oxidised products of their phenolic acids rosmarinic acid and lithospermic acid, also disable the thyroid-stimulating immunoglobulins of Graves’ disease, forming weakly-binding adducts with both TSH and the antibodies ^{5Reference 5Auf’mkolk et al. · 1985In vitroExtracts and auto-oxidized constituents of certain plants inhibit the receptor-binding and the biological activity of Graves’ immunoglobulins — in vitroView study →}.

An oral hydroethanolic L. europaeus extract in rats lowered T3, T4, TSH and LH for over 24 hours, which implies a central point of action rather than a purely thyroidal one ^{6Reference 6Winterhoff et al. · 1994AnimalEndocrine effects of Lycopus europaeus L. following oral application — animal model (rat)View study →}. A rat model of hyperthyroidism showed the extract reducing the cardiac signs ^{7Reference 7Vonhoff et al. · 2006AnimalExtract of Lycopus europaeus L. reduces cardiac signs of hyperthyroidism in rats — animal model (rat)View study →}.

The only human evidence is a small open-label, two-armed observational study in patients with suppressed TSH and hyperthyroid symptoms, in which a Lycopi europaei herba preparation significantly increased urinary T4 excretion and eased symptoms over three months ^{8Reference 8Beer et al. · 2008ObservationalLycopus europaeus (Gypsywort): effects on the thyroidal parameters and symptoms associated with thyroid function — human open-label observational studyView study →}. It was not randomised and had no placebo arm.

Almost all the research is on the European species, L. europaeus, and the two Western species are documented as pharmacologically near-identical. No randomised trial exists for either, and every result is tied to a specific freeze-dried or hydroethanolic extract rather than to a tea or tincture.