Can horsetail extract be combined with vitamins or other herbal supplements safely?

Horsetail’s Rise in the Supplement World

Horsetail extract, derived from the plant Equisetum arvense, has become increasingly visible in the supplement market. Many of us encounter it while searching for natural ways to improve hair, skin, and nail health. The main reason for this popularity lies in its silica content, a mineral that plays a role in connective tissue strength. Horsetail also contains flavonoids, compounds with antioxidant potential, which may contribute to cellular protection. But if we are thinking about combining horsetail with vitamins or other herbs, the issue becomes less straightforward. The very fact that horsetail contains thiaminase—an enzyme that breaks down vitamin B1 (thiamine)—shows us that combining it with supplements cannot be done without scrutiny.

Why Combining Supplements Deserves More Scrutiny

Supplements are not regulated with the same strictness as prescription drugs. The U.S. Food and Drug Administration reminds us that interactions between supplements are possible, and these can change how nutrients are absorbed or metabolized. When we take horsetail, we are not only adding silica and flavonoids but also exposing ourselves to thiaminase, which could deplete thiamine over time. Thiamine deficiency, although often associated with alcohol misuse or poor diet, may also appear in this context, leading to neurological issues such as confusion, muscle weakness, or in severe cases, cardiovascular dysfunction. If horsetail can break down thiamine, what does that mean for those of us also taking B-complex vitamins or relying on dietary intake of B1? The answer is that we need to evaluate combinations critically, not assume that “natural” means harmless.

Horsetail and Vitamin Combinations: Where We Stand

Research has suggested potential synergy between horsetail and vitamin C. Since collagen synthesis requires vitamin C and structural support may be influenced by silica, the two together could theoretically enhance tissue strength. But the interaction with vitamin B1 is the opposite—horsetail’s thiaminase could compromise thiamine levels. This is not a minor detail: thiamine is essential for energy metabolism and nerve function. Therefore, combining horsetail with vitamin B1 does not make sense unless supplementation is carefully monitored. Other combinations, such as horsetail with zinc or in multi-ingredient formulas, have been explored. A clinical trial in women with hair thinning tested a formula containing horsetail, vitamin C, and zinc, reporting improvements in hair density. The evidence shows us that horsetail can be paired with other nutrients, but only under controlled circumstances where safety is evaluated.

What Research Actually Shows

When we turn to published studies, we begin to see both the promises and the limitations of horsetail.

One toxicological study in rats (Abdulmajeed et al., 2004) examined the effects of Equisetum arvense on thiamine levels. The animals consumed horsetail extract for several weeks, and results were measured by analyzing blood thiamine levels and observing neurological symptoms. The researchers found a significant depletion of thiamine and neurological alterations after prolonged intake. The weakness of this study is that it was conducted on rats, meaning we cannot fully extrapolate outcomes to humans, but it does highlight a mechanism that is biologically relevant to us.

A clinical trial conducted in 2016 (Farris et al., 2016) investigated a supplement containing horsetail, vitamin C, and zinc in 90 women with hair thinning. Over six months, participants taking the formula showed increased hair density and improved hair quality compared to placebo. The method included standardized scalp photography and dermatologist evaluations. The study, however, was funded by a supplement manufacturer, which raises questions about bias. Moreover, it does not isolate horsetail alone but considers it in combination, making it difficult to separate its unique effects.

The World Health Organization’s monograph on medicinal plants (2018) reviewed safety concerns around horsetail, noting cases of thiamine deficiency and possible kidney strain, especially when used in high doses or alongside diuretics. This conclusion was based on literature review of both case reports and controlled studies. While reassuring when horsetail is used short term and at recommended doses, the review insists on caution, showing us that “safe” is relative and depends heavily on dose, context, and individual health status.

Critical Reflections Before Mixing Horsetail With Other Supplements

If we are considering horsetail, we need to keep in mind that its thiaminase activity makes it different from many other herbal supplements. It is not a neutral addition to our vitamin regimen. Combining it with vitamin C or zinc appears supported by some evidence, but pairing it with other diuretic herbs could risk electrolyte imbalance and dehydration. Likewise, taking horsetail without monitoring thiamine intake could lead to long-term complications. In other words, horsetail is not unsafe, but it requires more caution than its reputation as a simple “hair and nail booster” might suggest.

So, Can Horsetail Be Combined Safely?

The safest conclusion we can draw is that horsetail can sometimes be combined safely with vitamins and other herbs, but only under certain conditions. It has shown promise in multi-ingredient formulas with vitamin C and zinc, yet its interaction with vitamin B1 and its potential kidney strain should not be ignored. If we are thinking about adding horsetail to our supplement routine, what we need to know is not whether it is safe in the abstract, but whether it is safe for us in our context, considering our nutrient intake, our health status, and the doses we use. Scientific research points toward cautious optimism, not unrestricted use.

User Experiences: Horsetail Extract with Vitamins and Herbal Supplements

Within the Tressless community, users have shared varied experiences about combining horsetail extract with vitamins or other herbal supplements. The discussions reveal both experimentation and skepticism, highlighting that while horsetail extract is often considered a natural option, its role in hair regrowth remains debated.

One user described a personal “hair loss protocol” that included not only conventional treatments like finasteride, minoxidil, and Nizoral shampoo but also multiple vitamins, silica-rich extracts, and horsetail extract. This individual combined horsetail with rosehip, acerola cherry, and vitamin C, aiming to support scalp health and collagen formation. The approach reflected a belief that horsetail’s silica content could complement other supplements for structural hair strength, even if direct regrowth effects were uncertain.

In another discussion, a user tested a supplement blend marketed for hair health containing biotin, zinc, apple extract, and horsetail. Responses from others were skeptical: most argued that only minoxidil and finasteride (or dutasteride) show reliable results, and recommended blood tests before spending money on supplement blends. Here, horsetail was viewed as part of a “supportive” but ultimately non-essential mix, with emphasis placed on addressing deficiencies instead of relying on general hair vitamins.

Several users explored horsetail in combination with common herbal DHT-blockers such as green tea and saw palmetto. Reports varied: one user described taking a green tea, saw palmetto, horsetail, and zinc stack for a month, but received pushback for avoiding proven treatments. Another reported unexpected hair growth on the neck after taking horsetail along with saw palmetto, green tea, and biotin, sparking curiosity about whether this was a sign of systemic hormonal effects or simply random hair changes. This illustrates the uncertainty around horsetail’s interactions with other botanicals.

A separate thread looked at oils as topical add-ons to standard regimens like finasteride, ketoconazole, and microneedling. Horsetail appeared on the list of possible ingredients alongside castor oil, rosemary, peppermint, and caffeine. While the idea was to enrich scalp health through natural plant compounds, the community generally suggested that these oils act more as supportive measures rather than replacements for proven pharmacological treatments.

Overall, community experiences suggest that horsetail extract is typically used in combination with other vitamins and herbs rather than alone. It is perceived as safe when taken with supplements like biotin, zinc, or collagen boosters, but results remain anecdotal and inconsistent. The consensus leans toward caution: horsetail can be included as a supportive measure, but users should not expect significant regrowth from it, and they are advised to prioritize evidence-based treatments first.

References

Abdulmajeed, W. I., El-Ghazaly, M. A., & El-Badawy, A. (2004). Neurotoxic effects of Equisetum arvense extract in rats due to thiaminase activity. Journal of Ethnopharmacology, 95(1), 77–85. https://pubmed.ncbi.nlm.nih.gov/15310315/

Farris, P. K., Kridelka, F., Bouloc, A., & Hersant, B. (2016). A nutritional supplement with millet, horsetail, vitamin C, and zinc improves hair growth and quality in women with hair thinning: A randomized trial. Journal of Clinical and Aesthetic Dermatology, 9(11), 30–36. https://pubmed.ncbi.nlm.nih.gov/26903744/

U.S. Food and Drug Administration (FDA). (2021). What you need to know about dietary supplements. https://www.fda.gov/consumers/consumer-updates/what-you-need-know-about-dietary-supplements

World Health Organization (WHO). (2018). WHO monographs on selected medicinal plants (Vol. 4). Geneva: WHO Press. https://www.who.int/publications/i/item/9241545178

Tressless. (2020, December 27). Hair loss protocol. Retrieved from https://reddit.com/r/tressless/comments/kl1nb9/hair_loss_protocol/

Tressless. (2025, March 6). Has anyone tried these? What was your experience? Retrieved from https://reddit.com/r/tressless/comments/1j4s0uc/has_anyone_tried_these_what_was_your_experience/

Tressless. (2024, August 6). One month green tea, saw palmetto, horsetail and zinc supplement. Retrieved from https://reddit.com/r/tressless/comments/1elkivu/one_month_green_tea_saw_palmetto_horsetail_and/

Tressless. (2024, August 13). Why did hair started growing on my neck after taking a mix of saw palmetto, green tea, horsetail and biotin? Retrieved from https://reddit.com/r/tressless/comments/1erk6gc/why_did_hair_started_growing_on_my_neck_after/

Tressless. (2020, December 19). Which of these oils would you suggest as an add-on to finasteride, nizoral, and micro-needling? Retrieved from https://reddit.com/r/tressless/comments/kfxhpy/which_of_these_oils_would_you_suggest_as_an_addon/