The most common side effects of opioids are constipation, nausea and vomiting, and sedation. Others include psychiatric symptoms, dry mouth, urinary retention, pruritus, muscle cramps, irritability, drug resistance, and physical dependence. It is important to note that each patient’s response to opioid side effects varies greatly from patient to patient, so clinicians should be observant and give preventive treatment for some unavoidable side effects. Among the opioids, morphine is the most typical drug and its side effects are representative among opioids, so this section will discuss the adverse effects of morphine. (A) Nausea and vomiting It is currently believed that vomiting is the result of a complex reflex process triggered by stimulation of the vomiting center, which is located in the reticular formation area of the brain and receives stimulation from a variety of neural afferents. Data suggest that morphine-induced nausea and vomiting is caused by stimulation of the chemoreceptor trigger zone (CTZ) in the fourth ventricle, leading to excitation of the vomiting center. It is also associated with increased sensitivity of the vestibular nervous system, which is mainly manifested in active patients who are more symptomatic and more prone to nausea and vomiting. Data show that the incidence of nausea and vomiting in patients taking morphine: nausea 40% and vomiting 15%, while nausea has a higher incidence than vomiting. Patients with end-stage disease can induce or aggravate nausea and vomiting due to a variety of complications, such as liver and kidney dysfunction and electrolyte disorders. In addition, the incidence and severity of nausea and vomiting can be increased if patients are using biological agents, Chinese medicine or chemotherapy. The incidence of nausea and vomiting may be related to individual patient differences or the patient’s physical condition. （Constipation is the most common and persistent side effect of morphine, with an incidence of about 90-100%. Patients can hardly tolerate the effect of morphine-induced constipation, and the degree of constipation can be aggravated with the progress of the disease, such as intestinal obstruction (including paralytic intestinal obstruction caused by spinal cord compression), difficulty in eating and water intake due to anorexia, and restriction of patient’s activities. Therefore, while considering medications that cause constipation, look for other factors that cause constipation. (iii) Sedation may occur in the first few days of drug use, and may also occur after increasing the amount of drug used. When a patient becomes over-sedated with morphine, the first consideration is the cause, the degree of pain relief, other adverse effects and the degree of sedation. Mild sedation can be helpful in the recovery of a patient with pain and should not interfere too much with the patient’s sleep. Attention is needed to determine whether the patient’s sedation is related to chronic fatigue, whether the patient’s condition has become very severe, whether there is renal dysfunction or decompensation, whether there are liver function abnormalities, and whether there are problems with brain metastases. Also note whether the patient is taking the medication in the correct way and whether the drug delivery device used is malfunctioning, etc. In conclusion, the presence of sedation is not an indication for drug discontinuation, but requires a comprehensive evaluation of the patient before taking relatively reasonable treatment, which may be beneficial to the patient for pain relief and prevention of serious side effects. (iv) Respiratory depression Respiratory depression is one of the main obstacles that prevent patients from taking the full amount of medication. If patients have been using opioids for a long time, they generally have tolerance to morphine, which does not lead to respiratory depression. The presence of pain is a “physiological antagonist” to respiratory depression itself. In general, the observation of respiratory depression is more effective in determining the degree of sedation than in observing the number of breaths, because the blood concentration of respiratory depression is higher than that required for sedation. It should be noted that when pain is relieved by other methods but the drug is still administered at the original dose, it is likely to lead to respiratory depression, and timely reduction of the dose is the main way to prevent such problems. Patients taking morphine analgesia are very sensitive to antagonists, and the dose of naloxone should be determined according to the improvement in the patient’s respiratory rate, and the dose of naloxone should be gradually increased to try to reverse respiratory depression but not induce pain. (v) Pruritus is very rare and is related to the release of histamine due to morphine, and may also be related to the central nervous effect of morphine. It is usually self-limiting, and can be treated with antihistamines (e.g., diphenhydramine, breath minerals) and naloxone antagonism if itching is severe. (vi) Urinary retention Morphine rarely causes urinary retention. It is mainly caused by morphine causing spasm of the bladder sphincter and prompting the release of antidiuretic hormone. It is more common in elderly male patients with prostate enlargement. General medications for the prostate can relieve urinary retention, and heat applied to the lower abdomen and induction can be effective in some patients. Acupuncture can treat urinary retention. If necessary, catheterization can be performed and the urinary catheter can be retained for 2-3 days, and often the patient can urinate on his own after removal of the catheter. (vii) Psychiatric symptoms morphine at therapeutic doses can induce momentary blackouts, distraction, diminished thinking ability, indifference, reduced mobility, and in some patients, panic and awe. Some elderly people even appear delirium, such as the use of psychotropic drugs at the same time, the amount of psychotropic drugs should be reduced. (H) overdose each person’s sensitivity to the toxic effects of morphine varies greatly, long-term use of morphine drugs generally rarely morphine poisoning, never used morphine patients, when taking morphine 120mg or injecting morphine 30mg, will appear acute symptoms of poisoning, the patient confusion or coma, reduced respiration, cyanosis, decreased blood pressure, pupil narrowing. Treatment is mainly with naloxone to antagonize respiratory depression.