Equisetum arvense L.

Horsetail/Drug Interactions:

  • Alcohol (chronic use)Alcohol (chronic use): Chronic alcohol abusers may have thiamine deficiency. Because horsetail lowers thiamine levels, it may lead to neurologic damage in alcoholics.
  • Antiarrhythmic agentsAntiarrhythmic agents: Due to its potassium-depleting effects, horsetail may theoretically cause toxicity in patients with underlying cardiac arrhythmias or in those taking digoxin. Studies have demonstrated that horsetail likely does not affect blood pressure when taken orally (12).
  • Antidiabetic agentsAntidiabetic agents: A different horsetail species (Equisetum myriochaetum) has reportedly caused low blood sugar levels in patients with type 2 diabetes (10). Effects of Equisetum arvense are not clear.
  • Antigout agentsAntigout agents: Although horsetail increased the renal excretion of uric acid in one human trial, it also increased the formation of urine uric acid crystals (4). Therefore, horsetail may decrease the effects of antigout agents.
  • Cardiac glycosidesCardiac glycosides: Horsetail may theoretically compound cardiac glycoside toxicity due to its potassium-lowering properties. No reports of this interaction have been found in the available literature (12).
  • CNS stimulantsCNS stimulants: Nicotine, which is found in horsetail, is a CNS stimulant. Concomitant use of horsetail with other CNS stimulants may produce synergistic effects.
  • CorticosteroidsCorticosteroids: Use of horsetail with corticosteroids that decrease potassium may theoretically cause hypokalemia. However, there are no reports of this interaction in the available literature.
  • Digoxin, digitoxinDigoxin, digitoxin: Horsetail's potassium-depleting properties have been reported anecdotally. Hypokalemia may be dangerous in patients using cardiac glycosides, and potassium levels should be monitored in such individuals. There are no documented cases of this interaction in the available literature.
  • Disulfiram (Antabuse?)Disulfiram (Antabuse?): Many tinctures contain high levels of alcohol and may cause nausea or vomiting when taken with metronidazole (Flagyl?) or disulfiram (Antabuse?).
  • DiureticsDiuretics: Due to its constituents equisetonin and flavone glycosides, horsetail is believed to act as a weak diuretic and has preliminarily been demonstrated to act as a diuretic in humans (4). Theoretically, horsetail may thus reduce potassium levels. Use of horsetail with other diuretics may lead to hypokalemia or dehydration. However, there is a lack of reports of hypokalemia in the available literature.
  • Drugs used for osteoporosisDrugs used for osteoporosis: Because horsetail may increase bone density, it may have additive effects when taken in combination with osteoporosis agents (6). However, horsetail's anti-osteoporosis effects are not well established.
  • Gastrointestinal agents, miscellaneousGastrointestinal agents, miscellaneous: Some gastrointestinal agents, particularly laxatives, may increase the risk of potassium depletion, although literature searches have revealed no clinical cases.
  • Laxatives, stimulantLaxatives, stimulant: Stimulant laxatives used with horsetail may increase the risk of potassium depletion, although literature searches have revealed no clinical cases.
  • Metronidazole (Flagyl?)Metronidazole (Flagyl?): Many tinctures contain high levels of alcohol and may cause nausea or vomiting when taken with metronidazole (Flagyl?) or disulfiram (Antabuse?).
  • Neurologic agentsNeurologic agents: Horsetail may deplete human thiamine stores and cause irreversible neurologic damage such as Wernicke-Korsakoff syndrome (8).
  • NicotineNicotine: Due to the small amounts of nicotine found in horsetail, additive effects are possible when used with cigarettes or nicotine replacement therapy. Theoretically this may cause nicotine toxicity, which is characterized by fever, cold extremities, tachycardia, ataxia, muscle weakness, or weight loss. However, there are no available case reports documenting this reaction.
  • Potassium-depleting drugsPotassium-depleting drugs: Due to its potassium-depleting effects, horsetail may theoretically cause additive effects in patients taking potassium-depleting drugs (12).
  • SteroidsSteroids: Sterols contained in Equisetum arvense include beta-sitosterol, campesterol, isofucosterol, and trace amounts of cholesterol (13).

    • Horsetail/Herb/Supplement Interactions:

  • AntiarrhythmicsAntiarrhythmics: Due to its potassium-depleting effects, horsetail may theoretically cause toxicity among patients with underlying cardiac arrhythmias or those taking digoxin. Studies have demonstrated that horsetail likely does not affect blood pressure when taken orally (12).
  • Antigout herbs and supplementsAntigout herbs and supplements: Although horsetail increased the renal excretion of uric acid in one human trial, it also increased the formation of urine uric acid crystals (4). Therefore, horsetail may decrease the effects of antigout herbs or supplements.
  • AntioxidantsAntioxidants: Because in vitro research has shown that E. telmateia may be a useful source of antioxidants with huge scavenger ability, horsetail may have additive affects when taken with antioxidants (1).
  • Cardiac glycosidesCardiac glycosides: Horsetail may compound cardiac glycoside toxicity due to the potassium-lowering properties of the herb. There is a lack of reports supporting this interaction in the available literature.
  • DiureticsDiuretics: Due to its constituents equisetonin and flavone glycosides, horsetail is believed to act as a weak diuretic and has preliminarily been demonstrated to act as a diuretic in humans (4). Theoretically, horsetail may reduce potassium levels. Use of horsetail with other diuretics may lead to hypokalemia or dehydration. However, there are no reports of hypokalemia in the available literature.
  • Gastrointestinal herbs and supplementsGastrointestinal herbs and supplements: Some gastrointestinal herbs and supplements, particularly laxatives, may increase the risk of potassium depletion, although literature searches have revealed a lack of clinical cases.
  • HypoglycemicsHypoglycemics: A different horsetail species (Equisetum myriochaetum) has reportedly caused low blood sugar levels in people with type 2 diabetes (10). Effects of Equisetum arvense are not clear.
  • Laxatives, stimulantLaxatives, stimulant: Stimulant laxative herbs used with horsetail may increase the risk of potassium depletion, although literature searches have revealed a lack of clinical cases.
  • LicoriceLicorice: Licorice and horsetail both have potassium-depleting properties and may therefore have additive effects that result in hypokalemia. There is a lack of reports supporting this interaction in the available literature.
  • Neurologic herbs and supplementsNeurologic herbs and supplements: Horsetail may theoretically deplete human thiamine stores and cause irreversible neurologic damage such as Wernicke-Korsakoff syndrome (8).
  • Osteoporosis herbs/supplementsOsteoporosis herbs/supplements: Because horsetail may increase bone density, it may have additive effects when taken in combination with osteoporosis agents (6). However, horsetail's anti-osteoporosis effects are not well established.
  • Potassium depleting herbsPotassium depleting herbs: Due its potassium-depleting effects, horsetail may theoretically cause additive effects in patients taking potassium-depleting herbs and supplements (12).
  • SteroidsSteroids: Sterols contained in Equisetum arvense include beta-sitosterol, campesterol, isofucosterol, and trace amounts of cholesterol (13).
  • StimulantsStimulants: Nicotine contained in horsetail may act as a CNS stimulant. Concomitant use of horsetail with other CNS stimulants, such as ephedra, may produce additive or synergistic effects.

    • Horsetail/Food Interactions:

  • ThiamineThiamine: The silicon component of horsetail can break down thiamine and cause thiamine deficiency. This has been demonstrated only in animal models (8). Currently there is a lack of human clinical cases documenting this interaction.

    • Horsetail/Lab Interactions:

  • Serum creatinine, urine pH, urine uric acidSerum creatinine, urine pH, urine uric acid: In one human trial examining patients with a history of nephrolithiasis, an 18-24% statistically significant increase in diuresis was noted in people taking horsetail vs. baseline after 8-12 weeks; these individuals had an increase in glomerular filtration rate (GFR) of 22% (4). Horsetail was also noted to lower urine pH. Renal excretion of uric acid increased as did urine uric acid crystal formation.
  • Serum glucose levelsSerum glucose levels: A different horsetail species (Equisetum myriochaetum) has reportedly caused low blood sugar levels in patients with type 2 diabetes (10). Effects of Equisetum arvense are not clear.
  • Serum potassium levelsSerum potassium levels: Horsetail may possess potassium-depleting properties that may cause hypokalemia and subsequent electrolyte abnormalities.