Daily Allowed Dose of Horsetail
The recommended daily dose of horsetail (Equisetum arvense) extract is 900 mg/day, based on the highest quality clinical trial evidence demonstrating its potent diuretic effects comparable to hydrochlorothiazide 25 mg daily. 1
Evidence-Based Dosing
A randomized, double-blind, placebo-controlled trial in 36 healthy male volunteers established that horsetail extract at 900 mg/day produces diuretic effects (measured by 24-hour water balance) equivalent to hydrochlorothiazide 25 mg/day. 1
This 900 mg/day dose represents the only rigorously studied dosage in controlled human trials and should be considered the standard therapeutic dose. 1
Critical Safety Considerations
Volume Depletion and Hemodynamic Effects
Horsetail's potent diuretic activity can cause unintentional relative volume depletion, which may reduce renal plasma flow and subsequently decrease glomerular filtration rate. 1
The diuretic effect is significant enough to potentially cause hypotension, particularly in patients with compromised renal function or those taking other medications affecting blood pressure. 1
Contraindications and High-Risk Populations
Horsetail should be avoided entirely in patients with solitary kidneys, kidney donors, or those with any degree of renal insufficiency due to the heightened risk of nephrotoxicity from volume depletion in the setting of reduced renal reserve. 1
Pregnant women must avoid horsetail because it contains thiaminase, an enzyme that degrades thiamine (vitamin B1), and prolonged use can lead to vitamin B1 deficiency. 2 This risk is particularly severe when combined with alcohol exposure during pregnancy, as both deplete thiamine stores. 2
Drug Interactions
Horsetail may interact with antiretroviral medications (lamivudine/zidovudine/efavirenz and emtricitabine/tenofovir/efavirenz), potentially leading to virological breakthrough in HIV-positive patients previously stable on these regimens. 3
Patients on antiretroviral therapy should avoid horsetail supplementation until more data on these interactions become available. 3
Monitoring Requirements
Patients taking horsetail at 900 mg/day require monitoring for signs of volume depletion, including orthostatic hypotension, dizziness, decreased urine output, and electrolyte abnormalities. 1
Baseline and periodic assessment of renal function (serum creatinine, estimated GFR) is warranted, particularly if used for more than short-term therapy. 1
Blood pressure should be monitored regularly given the significant diuretic effect comparable to prescription thiazide diuretics. 1