Why does chemotherapy cause nausea or vomiting?

Chemotherapy is a commonly used treatment for cancer patients. As a chemical treatment method, it helps patients kill cancer cells but also causes great harm to the body. Many patients choose to give up chemotherapy during the treatment process because of the adverse reactions of chemotherapy. It's unbearable. The most common symptoms are nausea and vomiting. So why does chemotherapy cause nausea or vomiting?

The mechanism by which chemotherapy drugs induce nausea or vomiting is very complex, and it is generally believed that there is a vomiting reflex arc in its occurrence. There are two known central sites for vomiting. One is the vomiting center (VC), which is located in the medulla oblongata and is widely distributed. Experiments have shown that direct stimulation of this site with a microelectrode can induce vomiting. The other is the chemical emetic receptor zone (CTZ), which is located in the posterior zone of the fourth ventricle and is very sensitive to some chemicals from the blood or cerebrospinal fluid, but direct stimulation of this area with a microelectrode does not induce vomiting.

Scientists have discovered that emetic chemotherapy drugs can stimulate the gastrointestinal mucosa, causing mucosal damage, leading to the release of 5-hydroxytryptamine (5-HT) by chromaffin cells on the mucosa, which binds to 5-HT3 receptors in the internal organs, generating nerve impulses that are transmitted to the vomiting center and cause vomiting.

Chemotherapeutic drugs can also directly excite the vomiting center to cause vomiting or their metabolites can stimulate receptors in CTZ, which are then transmitted through neurotransmitter receptors to the vomiting center to induce vomiting. CTZ responds to a variety of stimuli, which act through a series of receptors, mainly including dopamine receptors, histamine receptors, muscarinic receptors, 5-HT3 receptors, etc.

In addition, when chemical drugs induce vomiting, many sensory afferent impulses enter the vomiting center, including those from the CTZ, cerebral cortex, and vagus nerve afferent branches of the gastrointestinal tract. In recent years, scientists have discovered through animal experiments that substance P also plays an important role in chemotherapy-induced nausea and vomiting by binding to the NK1 receptor. The use of NK1 receptor antagonists can inhibit vomiting, and this antiemetic effect has also been confirmed in clinical trials.

From this, we can infer that to suppress nausea and vomiting caused by chemotherapy, the commonly used drugs are mainly a series of receptor antagonists. In addition to the NK1 receptor antagonists mentioned above, there are also dopamine receptor antagonists, 5-HT3 receptor antagonists, etc.