Because Nolvadex is a selective estrogen receptor modulator and acts as a anti estrogen in the breast tissue of men and woman. But in the liver it acts as estrogen itself (agonist). Estrogen is very important in the liver to regulate serum cholesterol (natural balance of cholesterol). In the liver estrogen is responsible for increasing HDL (good cholesterol) and decreasing LDL (bad cholesterol). In other words although Nolvadex blocks estrogen when it comes to breast tissue, water retention and increase in bodyfat it acts the same as estrogen in the liver to keep cholesterol levels stable and keep bad cholesterol low and good cholesterol high. For exactly this reason Arimadex (that stops the conversion of estrogen totally) although beneficial for many reasons has a very bad effect on cholesterol levels if Arimadex is taken for to long. Its always best to alternate between Arimadex and Nolvadex when dealing with estrogen.
If you think there was an overdose, call your local poison control center or ER right away. Signs of a very bad reaction to the drug. These include wheezing; chest tightness; fever; itching; bad cough; blue or gray skin color; seizures; or swelling of face, lips, tongue, or throat. Blood in the urine. Not able to pass urine. Any bruising or bleeding. Very bad dizziness or passing out. Very loose stools (diarrhea). Very upset stomach or throwing up. Any rash. Side effect or health problem is not better or you are feeling worse.