Some studies have shown that cannabinoids are slightly better than conventional anti emetics such as metoclopramide, phenothiazines and haloperidol in the prevention of nausea and vomiting.[15] Cannabinoids are an option in affected people who are intolerant or refractory to 5-HT3 antagonists or steroids and aprepitant[15] as well as in refractory nausea and vomiting and rescue anti emetic therapy.[8] Prokinetic agents such as Metoclopramide[10] Dopamine receptor antagonists such as Phenothiazines (Prochlorperazine and chlorpromazine), haloperidol, olanzapine, and Levomepromazine, block D2 receptors found in the chemoreceptor trigger zone[10] Antihistaminic agents like Promethazine block H1 receptors in the vomiting center of the medulla, the vestibular nucleus, and the chemoreceptor trigger zone[10] Anticholinergic agents such as Scopolamine (Hyoscine) are used as anti emetics as they relax smooth muscle and reduce gastrointestinal secretions by blockade of muscarinic receptors. They may be useful in the management of terminal bowel obstruction[10] Somatostatin analoga such as Octreotide are used for the palliation of malignant bowel obstruction, especially when there is high output vomiting not responding to other measures[10] Cannabidiol is used as a palliative treatment (non-curative symptomatic treatment) and improves numerous symptoms that frequently appear during chemotherapy like nausea, vomiting, loss of appetite, physical pain or insomnia. Due to the large number of cannabinoid receptors ( CB1 and CB2 ) distributed throughout the gastrointestinal tract ( GI ) , these substances can help to control and treat many GI diseases where vomiting and nausea are frequent.[23]