The horsetail plant, or Equisetum arvense, is a potentially poisonous plant if eaten in large quantities.
 
The plant contains a compound called thiaminase, which breaks down vitamins before they have a chance to enter the body, and therefore leads to ill health. However, a human would have to consume this plant for days on end, with little else in the way of food or water, to become sick.
 
Bleeding
Gout
Frostbite
Heavy menstrual periods
Inability to control the bladder (incontinence)
Kidney or bladder stones
Osteoarthritis
Urinary tract infections
Weight loss
Wounds
 
Hair Growth 
Horsetail has an amino acid called cysteine in it. The herb also contains minerals such as selenium, which is known to enhance hair growth. Certain chemicals in horsetail are thought to lower inflammation. They might also help the body make more substances that boost the immune system (antioxidants). Horsetail also has silica and silicon in it. These minerals work together to strengthen the hair and nails. They also help the body make healthy bone tissue. Selenium, another mineral that has been shown to help hair grow, is also found in horsetail.
 
Horsetail has nicotine in it. You should not use horsetail if you use nicotine gum or nicotine replacement patches.
 
Blood Sugar
 
Osteoporosis
 
https://www.verywellhealth.com/horsetail-4692253