Please note that many horsetail supplements, which are used for everything from kidney health to bone, sugar and hair health often has thiaminase in it. This lowers thiamine in body. (link below)
Special Warning
Horsetail has an enzyme called thiaminase in it. The enzyme breaks down thiamine, which is also called vitamin B1. When thiamine is broken down, it becomes useless to the body.
If you take too much horsetail or take it for a long time, you might not have enough thiamine in your body (thiamine deficiency).
Not FDA Approved
Some commercial horsetail products say that they do not have thiaminase in them. However, herbal supplements are not regulated by the FDA. That means the information on these products' labels can be wrong.
Even if a product does not have thiaminase in it, there is not enough evidence to prove that using a thiaminase-free horsetail product is safe and effective.
Contraindications
A contraindication means that you should not take a medication or supplement because it might cause a bad reaction. Medical conditions, medications, other products you use, and treatments can all be contraindications.
Horsetail has several known contraindications. If any of these situations apply to you, do not use horsetail.
Alcohol use disorders: Horsetail makes the body less able to use thiamine. Drinking a lot of alcohol can make you more likely to have a thiamine deficiency.
Thiamine deficiency: Horsetail breaks thiamine in half. This makes it useless in the body. If this happens, you may not have enough thiamine to meet your body's needs (thiamine deficiency). Your provider might want you to take a B complex or multivitamin daily if you use horsetail to help prevent a thiamine deficiency.
Pregnancy or breastfeeding: There has not been enough research on using horsetail when you are pregnant or breastfeeding to show that it is safe.
Diabetes: Horsetail is thought to lower blood sugar. Having blood sugar levels that are too low is called hypoglycemia. If a person with diabetes gets very low blood sugar levels, it can be life-threatening.
Low potassium: Horsetail has a "fluid-flushing" effect. This is called a diuretic. When you lose a lot of fluid from your body, you also lose an important nutrient called potassium. If your levels of potassium get too low, it's called hypokalemia. This condition can be very dangerous because it can make your heart not work properly.