http://ezinearticles.com/?Horsetail---Uses-and-Side-Effects&id=1049035
Hazards
Side effects of horsetail include electrolyte imbalance, skin irritation from topical use, thiamine deficiency from long-term use, and symptoms of nicotine poisoning and toxicity including nausea and vomiting, muscle weakness, abnormal pulse rate, fever, and ataxia. Use of horsetail with benzodiazepines, disulfiram, or metronidazole may cause a disulfiram-like reaction. Horsetail may increase digitalis toxicity as a result of potassium loss with diuretic effect. When it's used with potassium-wasting drugs (including corticosteroids, diuretics, and laxative stimulants), there's an increased risk of hypokalemia. Overuse of licorice with horsetail may increase potassium depletion and risk of cardiac toxicity. Excessive alcohol consumption while horsetail is being used may lead to thiamine deficiency.
Pregnant patients, breast-feeding patients, those with impaired heart or kidney function, those with liver problems, those who are taking a cardiac glycoside, and those who have a history or potential of thiamine deficiency (for example, alcoholic patients) should avoid using horsetail.
Safety Risk The liquid extract contains 25% alcohol and there fore shouldn't be used with disulfiram, metronidazole, and benzodiazepines.
Clinical considerations
Horsetail dosage varies with the formulation. Large amounts may cause a toxic reaction.
The dried, powdered extract is more concentrated than stem alone.
Monitor patient's serum potassium level.
Assess patient for signs and symptoms of hypokalemia, including weakness, muscle flaccidity, and abnormal ECG results.
Horsetail shouldn't be used for extended periods because of the potential for toxic reaction and thiamine depletion.
Instruct patients to stop taking horsetail immediately if signs or symptoms of nicotine toxicity (muscle weakness, abnormal pulse rate, fever, ataxia, and cold extremities) or potassium depletion (muscle cramping, irritability, or weakness) occur.
If patient is pregnant or breast-feeding, advise her not to use horsetail.
Advise patients taking a potassium wasting diuretic, a cardiac glycoside (Lanoxin), a corticosteroid, or licorice not to use horsetail.
Tell patient to notify pharmacist of any herbal or dietary supplement that he's taking when obtaining a new prescription.
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