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Emetics and antiemetics are substances which cause opposite effects on the body. Emetics are used to induce vomiting, while antiemetics are used to treat nausea and vomiting. The antiemetics are most commonly used in modern medicine, emetics being used mainly in some cases of poisoning. There are a number of different drugs that act as emetics and antiemetics and they differ in their mechanism of action, or how they work.
Nausea is the feeling of wanting to vomit and vomiting is the expulsion of the stomach's contents out of the mouth. There are a wide variety of causes of both nausea and vomiting, including viral illnesses, sea sickness or motion sickness and medicines such as chemotherapy. Peripheral and central actions are both involved in vomiting so it can be triggered by the stomach, blood, balancing organs or brain. External factors, like seeing somebody else vomit or witnessing something disturbing can also cause vomiting.
While emetics and antiemetics have opposite effects, they both work on the vomiting center, which is located in the hypothalamus in the brain and is controlled by the chemo-effector trigger zone (CETZ) which responds to the triggers listed above. Antiemetics work at different stages of this process, to inhibit the vomiting. Depending on the cause of the nausea and vomiting, the most suitable antiemetic will be chosen. In the case of emetics, they work by stimulating the CETZ, causing the person to vomit.
Emetics were commonly used for a variety of disorders in old medicine, but their use has diminished, mainly being used in the case of some poisonings or overdose. In some cases, where removal of the poison is necessary and does not pose extra risk in the process of vomiting, an emetic, such as ipecac, may be given. This should only be done under medical supervision as some poisons, such as acid, may cause more damage if vomiting is induced.
Of emetics and antiemetics, the antiemetics are far more widely used in modern medicine, in a wide range of settings. A number of different medicines may act as antiemetics, each working by different mechanisms. The most suitable antiemetic to use should be discussed with a pharmacist or doctor who will take into consideration the cause of the nausea and vomiting. Commonly used antiemetics include antihistamines like promethazine and cyclizine, and 5HT-3 antagonists such as ondansetron and granisetron.
As with any medication, both emetics and antiemetics may have interactions with other medications, be contraindicated in patients with some underlying clinical conditions and potentially cause adverse side effects. These should all be discussed with a health care professional before using them. Nausea and vomiting in pregnancy is common and this should also be discussed with the pharmacist to ensure the safest antiemetic in pregnancy is used.
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