Ashina, S., Mitsikostas, D. D., Lee, M. J., Yamani, N., Wang, S.-J., Messina, R., Ashina, H., Buse, D. C., Pozo-Rosich, P., Jensen, R. H., Diener, H.-C., & Lipton, R. B. (2021). Tension-type headache. Nature Reviews Disease Primers, 7(1), 24. https://doi.org/10.1038/s41572-021-00257-2
Tier 2Peer-reviewed disease primer
Establishes tension-type headache as the most common primary headache and psychological stress as its most frequently reported trigger. Used for the framing, not for any treatment claim.
Cathcart, S., Winefield, A. H., Lushington, K., & Rolan, P. (2010). Stress and tension-type headache mechanisms. Cephalalgia, 30(10), 1250-1267. https://doi.org/10.1177/0333102410362927
Tier 2Peer-reviewed review
Reviews how psychological stress contributes to tension-type headache through muscle and central pain pathways. Mechanism evidence, not herbal-intervention evidence.
Verhagen, A. P., Damen, L., Berger, M. Y., Passchier, J., & Koes, B. W. (2009). Behavioral treatments of chronic tension-type headache in adults: Are they beneficial? CNS Neuroscience & Therapeutics, 15(2), 183-205. https://doi.org/10.1111/j.1755-5949.2009.00077.x
Tier 2Systematic review (44 RCTs)
Found no clear evidence that relaxation, biofeedback or CBT outperform waiting-list or placebo for tension-type headache. A contrarian-honesty citation, used to rule out any 'tea is as good as biofeedback' extrapolation.
Göbel, H., Fresenius, J., Heinze, A., Dworschak, M., & Soyka, D. (1996). Effectiveness of Oleum menthae piperitae and paracetamol in therapy of headache of the tension type. Der Nervenarzt, 67(8), 672-681.
Tier 2Randomised double-blind crossover trial
Topical 10% peppermint oil reduced tension-headache intensity versus placebo. INFORMATIONAL ONLY: peppermint oil is topical and is not an ingredient in Sippo teas, cited to show the strongest direct evidence is for something we do not sell.
Amsterdam, J. D., Li, Y., Soeller, I., Rockwell, K., Mao, J. J., & Shults, J. (2009). A randomized, double-blind, placebo-controlled trial of oral Matricaria recutita (chamomile) extract therapy for generalized anxiety disorder. Journal of Clinical Psychopharmacology, 29(4), 378-382. https://doi.org/10.1097/JCP.0b013e3181ac935c
Tier 2Randomised controlled trial
Chamomile extract reduced generalised anxiety symptoms versus placebo over 8 weeks. Used a standardised extract, not tea, so cited for the calming mechanism behind a soothing ritual, not as proof a teabag treats anything.
Ghazizadeh, J., Sadigh-Eteghad, S., Marx, W., Fakhari, A., Hamedeyazdan, S., Torbati, M., Taheri-Tarighi, S., Araj-Khodaei, M., & Mirghafourvand, M. (2021). The effects of lemon balm (Melissa officinalis L.) on depression and anxiety in clinical trials: A systematic review and meta-analysis. Phytotherapy Research, 35(12), 6690-6705. https://doi.org/10.1002/ptr.7252
Tier 2Systematic review and meta-analysis
Pooled clinical trials found lemon balm improved anxiety and depression scores versus placebo. The strongest evidence is for calm/mood; we extend it to evening wind-down cautiously.