Horsetail is used for edema, kidney and bladder stones, UTI, and general disturbances of the kidney and bladder. It is also used for balding; tuberculosis; jaundice; hepatitis; brittle fingernails; joint diseases; gout; osteoarthritis; weak bones (osteoporosis); frostbite; weight loss; heavy menstrual periods; and uncontrolled bleeding of the nose, lung, or stomach. Horsetail is applied directly to the skin to treat wounds and burns.

Cautions and Side Effects of Horsetail:Pregnancy and breast-feeding: Avoid use of Horsetail.Alcoholism: People who are alcoholics are generally also thiamine deficient. Taking horsetail might make thiamine deficiency worse.

Diabetes: Horsetail might lower blood sugar levels in people with diabetes. Watch for signs of low blood sugar (hypoglycemia) and monitor your blood sugar carefully if you have diabetes and use horsetail.Low potassium levels (hypokalemia): 
Horsetail might flush potassium out of the body, possibly leading to potassium levels that are too low. Until more is known, use horsetail with caution if you are at risk for potassium deficiency.
Low thiamine levels (thiamine deficiency): There is a concern that horsetail could make thiamine deficiency worse.