Horsetail [Discontinued] by Herb Pharm

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Androgenic alopecia. Although there is interest in using oral horsetail for alopecia, there is insufficient reliable information about the clinical effects of horsetail for this condition.
• Hypertension. Oral horsetail seems to reduce blood pressure in patients with hypertension. Details: A clinical trial in patients with stage 1 systemic arterial hypertension shows that taking horsetail extract 900 mg daily for 3 months decreases systolic and diastolic blood pressure by 13 mmHg and 8 mmHg, respectively, and is similarly effective to hydrochlorothiazide 25 mg daily (108849). The validity of this finding is limited due to high withdrawal rates and low adherence to treatment protocols.
• Kidney stones (nephrolithiasis). Although there is interest in using oral horsetail for kidney stones, there is insufficient reliable information about the clinical effects of horsetail for this condition.
• Obesity. Although there is interest in using oral horsetail for weight loss, there is insufficient reliable information about the clinical effects of horsetail for this purpose.
• Osteoporosis. It is unclear if oral horsetail is beneficial for osteoporosis. Details: Preliminary clinical research shows that taking two tablets of either dried horsetail extract or a specific combination of horsetail extract with calcium (Osteosil Calcium) daily for 2-month intervals separated by 2 weeks of no treatment for up to one year can increase bone density when compared with no treatment in postmenopausal patients with osteoporosis. The effect of horsetail extract plus calcium (Osteosil Calcium) seems to be greater than the effect of dried horsetail extract alone (55578).
• Tonsillitis. Oral horsetail has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research in children with acute non-bacterial tonsillitis shows that taking a specific combination product (Imupret) for 10 days in addition to standard symptomatic therapy accelerates recovery by a small amount when compared with symptomatic therapy alone. Overall treatment response after 10 days occurred in 82% of patients taking the combination product compared with 65% of patients receiving symptomatic therapy alone. Withdrawal from antipyretic drugs occurred approximately one day earlier in children using the horsetail product. Per 100 grams, Imupret provides 29 grams of an alcoholic extract produced from horsetail 0.5 grams, marshmallow root 0.4 grams, chamomile flowers 0.3 grams, walnut leaves 0.4 grams, English walnut leaves 0.4 grams, yarrow 0.4 grams, oak bark 0.2 grams, and dandelion 0.4 grams. In children aged 6-11 years, 15 drops 6 times daily for 5 days and then 15 drops 3 times daily for 5 days was used. In children aged 12-18 years, 25 drops 6 times daily for 10 days was used. (100347). Due to the small difference between the two groups and the open-label design, the clinical relevance of this study is unclear. Also, it is unclear if these benefits are due to horsetail, the other ingredients, or the combination.
• Urinary incontinence. Oral horsetail has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research shows that taking a specific supplement (Urox, Seipel Group) 840 mg, containing a combination of horsetail stem, three-leaf caper, and lindera root daily with food for 8 weeks modestly decreases urinary frequency, stress incontinence, and urgency incontinence when compared with placebo in patients with urinary incontinence and/or overactive bladder (97575). It is unclear if these effects are due to horsetail, the other ingredients, or the combination.
• Urinary tract infections (UTIs). Although there is interest in using oral horsetail for UTIs, there is insufficient reliable information about the clinical effects of horsetail for this condition. More evidence is needed to rate horsetail for these uses.

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POSSIBLY UNSAFE ...when horsetail products containing thiaminase are used orally, long-term. Thiaminase is an enzyme that destroys thiamine, which could theoretically lead to thiamine deficiency. In Canada, horsetail products are required to be thiaminase-free (105301).

PREGNANCY AND LACTATION:
Insufficient reliable information available; avoid using.

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ANTIDIABETES DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, taking horsetail with antidiabetes drugs might increase the risk of hypoglycemia.  Details Equisetum myriochaetum has demonstrated hypoglycemic activity in clinical research (13576). In an animal diabetic model, Equisetum giganteum had hypoglycemic effects (105300). It is unclear whether other horsetail species have hypoglycemic effects.

DIURETIC DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, taking horsetail with diuretic drugs might increase potassium loss and the risk of hypokalemia.  Details Laboratory research shows that various species of horsetail have diuretic properties (13574,13575). Due to its diuretic effects, there has been concern that taking horsetail along with potassium-depleting diuretics might increase the risk for hypokalemia. However, pharmacokinetic research in humans shows that taking horsetail 900 mg daily for 4 days does not affect urinary excretion of electrolytes, including potassium and sodium, despite having a diuretic effect similar to taking hydrochlorothiazide 25 mg daily (92288). It is unclear if taking horsetail for a longer duration would affect electrolyte levels. Until more is known, use with caution.

EFAVIRENZ (SUSTIVA) Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D Theoretically, horsetail might decrease the levels and clinical effects of efavirenz.  Details In two case reports, patients were found to have detectable viral loads when taking horsetail-containing supplements along with an antiretroviral regimen that included efavirenz. In one case, the antiretroviral regimen included zidovudine, lamivudine, and efavirenz; in the other case, the regimen consisted of emtricitabine, tenofovir disoproxil fumarate, and efavirenz. One month after discontinuing horsetail, the viral loads became undetectable in both cases. The exact mechanism of this interaction is unknown (97573). It is also unclear if this interaction is specific to efavirenz or if it is related to various components of antiretroviral therapy.

LITHIUM Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, horsetail might increase the levels and adverse effects of lithium.  Details Animal research suggests that horsetail has diuretic properties (13574). Theoretically, due to these potential diuretic effects, horsetail might reduce excretion and increase levels of lithium. The dose of lithium might need to be decreased.

NUCLEOSIDE REVERSE TRANSCRIPTASE INHIBITORS (NRTIs) Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D Theoretically, horsetail might decrease the levels and clinical effects of NRTIs.  Details In two case reports, patients were found to have detectable viral loads when taking horsetail-containing supplements along with an antiretroviral therapy. In one case, the antiretroviral regimen included zidovudine, lamivudine, and efavirenz; in the other case, the regimen consisted of emtricitabine, tenofovir disoproxil fumarate, and efavirenz. One month after discontinuing the supplement, the viral loads became undetectable in both cases. The exact mechanism of these interactions is unknown (97573). It is also unclear if these interactions are specific to NRTIs or if they are related to various components of antiretroviral therapy.

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General ...There is limited clinical research evaluating the safety of horsetail.
Most Common Adverse Effects:
Orally: Abdominal distension, increased bowel movements, and nausea.

Dermatologic ...In one case report, a patient developed seborrheic dermatitis after topical application of horsetail, requiring treatment with local epinephrine and oral antihistamines. The nicotine component of horsetail was determined to be the likely cause of this reaction (13563).

Gastrointestinal ...Orally, horsetail has been associated with mild gastrointestinal side effects including abdominal distension, increased frequency of bowel movements, and nausea (55576). Orally, chronic consumption of horsetail infusion has been associated with acute pancreatitis. In a case report, a 56-year-old female presenting with recurrent mild acute pancreatitis every 6-7 months, previously thought to be drug-induced, discontinued ingesting horsetail infusions. The patient had a history of bilateral adrenal gland removal and was being treated for hypertension, dyslipidemia, and hormone replacement, and then self-medicated with horsetail infusions. After discontinuing horsetail infusions, there were no further recurrences of pancreatitis during a 14-month follow-up (97574).

Hepatic ...In one case report, a patient with asymptomatic hepatitis B developed symptomatic liver failure following consumption of boiled horsetail juice 500 mL daily for 2 weeks. Liver enzymes returned to normal following discontinuation of the juice (92291). It is not known if the horsetail juice was contaminated or mixed with other ingredients.

Immunologic ...Horsetail has been associated with cross-allergenicity with carrots (13577).

Renal ...There are at least 4 case reports of hyponatremia thought to be at least partially associated with horsetail consumption. In one case report, an elderly patient who had taken oral horsetail 15 mg daily for 10 years presented with hyponatremia and syndrome of inappropriate secretion of antidiuretic hormone (SIADH) secondary to reduced oral intake and nausea for the previous 2 days. Horsetail was thought to be a contributing factor. The patient's symptoms resolved after 5 days of treatment with oral sodium chloride and fluid restriction (108851).

Other ...Crude horsetail contains thiaminase, which can cause thiamine deficiency with prolonged consumption. Canadian Equisetum arvense products are required to be certified as free from thiaminase-like activity (55579,105301). In one case report, the development of autism in a child exposed to both horsetail and alcohol during pregnancy was thought to be caused by thiamine deficiency attributed to this combination (92292). However, it is not known if other genetic or environmental factors were involved in the development of this condition in utero.

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