The main laxatives before having a colonoscopy are polyethylene glycol electrolyte bulk and magnesium sulfate. Different drugs may be used in different ways and need to be analyzed specifically. 1. Polyethylene glycol electrolyte bulk: usually start the diarrhea one day before the colonoscopy. Dissolve one sachet of polyethylene glycol electrolyte bulk in about 1,000 ml of lukewarm water and drink small amounts several times within one hour. Repeat this procedure about three times until the feces are clear and watery, with no or only a small amount of fecal residue. 2. Magnesium sulphate: usually dissolve one packet of magnesium sulphate in 1000 ml of boiling water and take it the day before the examination, after taking it, drink more water until the feces is watery, that is, the purging is completed. Note that if there is an acute abdomen, women in menstruation and other conditions are generally not suitable for oral intestinal cleansing of magnesium sulfate, so as not to cause adverse reactions. The use of specific drugs should be used in accordance with medical advice, avoid self-medication.