The main reason why taking diet pills can cause delayed menstruation is that diet pills tend to cause diarrhea. Prolonged diarrhea easily leads to excessive loss of tissue fluid in the body, and nutrients in the body will also be excreted with feces, resulting in the body being in a slight malnutrition, causing delayed menstruation. Clinical use of diet pills should be taken according to the doctor’s instructions, avoiding large amounts, which can easily cause short-term dehydration and lead to electrolyte imbalance, causing hypokalemia and hyponatremia. If there is a delay in menstruation, the drug should be stopped immediately and menstruation will come normally next month. If delayed menstruation lasts for more than three months, prompt treatment is recommended. It is recommended to take estrogenic drugs under the guidance of a doctor to establish the menstrual cycle so as to restore normal menstruation.