Short answer. The strongest evidence is a 2018 double-blind, randomised, placebo-controlled trial in Nutrients: 140 healthy adults aged 50 to 70 took a standardised Sideritis scardica extract for 28 days. At the higher dose the researchers measured improved attention accuracy, a large reduction in state anxiety versus placebo, and increased cerebral blood flow after the first dose. Blood pressure was unaffected. The trial used a standardised extract at fixed doses rather than a brewed pot, which is the honest limit on what a cup at home can be said to do.

The trial, in plain numbers

Wightman and colleagues ran a double-blind, randomised, placebo-controlled, parallel-groups study and published it in Nutrients in 2018. Participants were healthy adults aged 50 to 70, mean age around 60. They received 475 mg or 950 mg of a standardised Sideritis scardica extract, a Ginkgo biloba active control, or placebo, and were assessed on day 1 and again after 28 days of daily use.

At 950 mg the results reached statistical significance in three separate places. Attention accuracy improved: false alarms on a rapid visual information processing task dropped against placebo on day 28. Picture recognition accuracy was higher than the Ginkgo control on both testing days. State anxiety fell by roughly three points on the standard STAI scale against placebo, an effect size the authors describe as large.

On the first dose, near-infrared spectroscopy showed increased oxygenated haemoglobin and oxygen saturation in the frontal cortex at both doses — measurably more blood flow to working brain tissue. That acute effect was not still present at day 28, and the authors attribute the later cognitive gains mainly to the drop in anxiety rather than to blood flow.

  • Design: double-blind, randomised, placebo-controlled, parallel groups
  • Participants: 140 healthy adults, aged 50 to 70
  • Doses: 475 mg and 950 mg standardised extract, daily, 28 days
  • Significant: attention accuracy, state anxiety, acute cerebral blood flow
  • Not significant: blood pressure

A second trial: antioxidant capacity, measured in blood

A separate randomised, double-blind, placebo-controlled study published in Molecules in 2024 took a different angle. Twenty-eight healthy adults took 1,500 mg a day of a characterised Sideritis scardica extract for four weeks while the researchers tracked blood markers rather than cognitive tests.

Total antioxidant capacity in plasma rose 11.6 per cent, and lipid peroxidation — the marker of oxidative damage to fats in the blood — fell 10.8 per cent. Both results were statistically significant. Systolic blood pressure fell by almost 11 mmHg, resting heart rate dropped, and two liver enzymes came down. Glucose, the full cholesterol panel, blood counts and several other redox markers did not move.

This is where "antioxidant" stops being a marketing word and becomes a measurement. It is also a small study — 28 people, 14 per group — and we would rather say that than let you assume it is bigger than it is.

  • Total antioxidant capacity: +11.6 per cent
  • Lipid peroxidation (TBARS): −10.8 per cent
  • Systolic blood pressure: −10.9 mmHg
  • No change: glucose, cholesterol panel, blood counts
  • Sample: 28 healthy adults, four weeks

Where the two trials disagree

The 2018 trial found no effect on blood pressure at all. The 2024 trial found a substantial fall in systolic pressure. The extracts differ, the doses differ, the samples differ, and nobody has reconciled them.

We are not going to pick the flattering result. If you see mountain tea sold as a blood-pressure remedy, note that the larger of the two trials measured blood pressure and found nothing. That is the kind of detail a seller drops and a reader deserves.

What is animal research, and stays labelled as such

Sideritis scardica also has a well-known 2012 study in Planta Medica showing anti-inflammatory effects in rats comparable to indomethacin, and gastroprotective effects comparable to ranitidine. It is good pharmacology and it is the likely reason the plant earned its traditional reputation for the stomach.

It is also rats. We mention it because it is real and because leaving it out would be its own kind of dishonesty, but it is not a human result, it is not a reason to drink the tea for inflammation, and we will not dress it up as one. The same goes for laboratory work on verbascoside, the plant’s main polyphenol, in cell culture.

Where the evidence stops, and why we say so

Both human trials tested standardised, characterised extracts at measured doses. A pot of whole stems on a domestic stove is not that, and no study has established what dose of which compounds ends up in a home-brewed cup. Anyone who tells you a mug of mountain tea reproduces a clinical result is selling you something.

What is fair to say is this: the plant behind the tradition has real human trial evidence behind it, from two independent randomised controlled studies, and the outcomes measured were attention, anxiety, blood flow, antioxidant capacity and blood pressure — not immunity, not detoxification, not cures. We do not claim what was not measured.

We also correct our own record here. An earlier version of this page cited a PubMed identifier that turns out to point at an unrelated journal editorial about a journal’s tenth birthday. It was wrong, it is gone, and every citation on this site has since been fetched and checked against the claim it supports.

Read them yourself

Wightman EL, Jackson PA, Khan J, Forster J, Heiner F, Feistel B, Suarez CG, Pischel I, Kennedy DO. "The Acute and Chronic Cognitive and Cerebral Blood Flow Effects of a Sideritis scardica (Greek Mountain Tea) Extract: A Double Blind, Randomized, Placebo Controlled, Parallel Groups Study in Healthy Humans." Nutrients, 2018;10(8):955. doi:10.3390/nu10080955 — https://pmc.ncbi.nlm.nih.gov/articles/PMC6116054/

Papanikolaou K, et al. "Characterization of the Sideritis scardica Extract SidTea+ and Its Effect on Physiological Profile, Metabolic Health and Redox Biomarkers in Healthy Adults: A Randomized, Double-Blind, Placebo-Controlled Study." Molecules, 2024;29(5):1113. doi:10.3390/molecules29051113 — https://pmc.ncbi.nlm.nih.gov/articles/PMC10934388/

Tadić VM, Jeremic I, Dobric S, Isakovic A, Markovic I, Trajkovic V. "Anti-inflammatory, gastroprotective, and cytotoxic effects of Sideritis scardica extracts." Planta Medica, 2012;78(5):415–427. doi:10.1055/s-0031-1298172 — animal study, https://pubmed.ncbi.nlm.nih.gov/22274814/

Moussavi N, Azizullah H, Malterud KE, Inngjerdingen KT, Wangensteen H. "Immunomodulating polyphenols from Sideritis scardica." Journal of Functional Foods, 2022;96:105197. doi:10.1016/j.jff.2022.105197 — cell-culture study