Horsetail Side Effects and Warnings

Safety Issues

Noticeable side effects from standard dosages of horsetail tea are rare. However, horsetail contains an enzyme that damages vitamin B 1 (thiamin) and has caused severe illness and even death in livestock that consumed too much of it. ¹ In Canada, horsetail products are required to undergo heating or other forms of processing to inactivate this harmful constituent.

Also, perhaps because horsetail contains low levels of nicotine, children have been known to become seriously ill from using the branches as blow guns. ² This plant can also concentrate toxic metals present in its environment.

For all of the above reasons, horsetail is not recommended for young children, pregnant or nursing women, or those with severe kidney or liver disease.

Individuals taking the medication lithium should use herbal diuretics such as horsetail only under the supervision of a physician, as becoming dehydrated while taking this medication can be dangerous. ³ Horsetail may also cause loss of potassium, which may be dangerous for people taking drugs in the digitalis family. ⁴

Interactions You Should Know About

If you are taking

• Drugs in the digitalis family :Use horsetail only under medical supervision.

• Lithium :Do not use horsetail except under the supervision of a physician.