This is the protocol for Nausea/Vomiting:



Let’s break it down!

Nausea/vomiting (N/V) is one of the most common, non-specific complaints among both soldiers and just people in general.  Although vomiting is an evolutionary mechanism designed to expel unwanted material, it does have it’s risks.  Vomiting can cause dehydration, electrolyte disturbances, damage to the throat/teeth, aspiration, etc.   It can be a condition in and of itself, but usually, it comes secondary to some other illness or injury.  

To be able to treat N/V appropriately, we have to understand the various pathological pathways associated with it.  For starters, the entire act of vomiting is centered around the vomiting center, which a group of loosely organized neurons in the medulla oblongata.  Before inducing the act of vomiting, it will receive receptor-based messages from one of the following places:

  • Stomach/Intestines: serotonin type 3 receptors (5HT3) send N/V signals to the brain via the vagus nerve whenever they become stretched (from bloating, overeating, etc.) or irritated (excessive bile, etc.)


  • Chemoreceptor Trigger Zone (CTZ): Located near the vomiting center and sends messages via Dopamine Type 2 receptors (DA2) and Substance type P (NK1) whenever there is a chemical or toxic disturbance in the body, such as opiates, chemotherapy agents, etc.


  • Vestibular System: part of the inner ear that’s responsible for being able to detect motion and help us understand where we are in space.  When there is a disturbance, messages will be sent via Histamine 1 (H1) receptors and Muscarinic (M1) receptors.  


  • “Higher Centers”: This includes everything else.  Emotions, migraines, smells, sights can all cause feelings of nausea that can lead to vomiting.  The mechanisms behind these causes are not clear yet.  


For a more in-depth review, check out the video below:

We’ve all seen people when they’re about to barf all over the floor…. pale, weak, dizzy, holding their tummy.  But there are certain red flags that you should be looking out for that might prompt you to utilize another protocol on top of this one.  Here are a few to look out for:

  • Excessive blood in vomit: may indicate a peptic ulcer, Mallory-Weiss tear (tear in the esophagus), or upper GI bleed


  • Vomiting after a traumatic injury: may indicate a life-threatening traumatic brain injury


  • Severe abdominal pain: May indicate an acute infection or inflammation of abdominal organs.


  • Non-stop vomiting w/o eating: presents a risk for severe dehydration

One of the more common causes of nausea is related to dyspepsia, otherwise known as “indigestion”.  Although some amount of acid in the stomach is tolerable, foods that are fatty, greasy, or spicy can cause excessive production of acid, which leads to an irritation of the stomach lining.  Too much caffeine, alcohol, chocolate, and carbonated beverages can also cause this.  Most cases don’t typically result in vomiting, but the feeling of an “upset stomach” can often lead to nausea.

We have two medications that we can use to protect the stomach from excessive acid production: Calcium Carbonate and Bismuth Subsalicylate 

Calcium Carbonate (TUMS)

Works by neutralizing the acidity in the gut.  Gastric acid has a pH of roughly 1.5-3.5, which can overwhelm the stomach.  Calcium carbonate is a basic substance with a pH of 9.91, so adding this to the mix of gastric acid will help lower the acidity and thus reduce nausea and dyspepsia.  It’s a very safe medication and it works right away!

Bismuth Subsalicylate (Pepto-Bismol)

This also works as a mild antacid, like TUMS, but most functions by providing a smooth coating around the lining of the stomach so that the gastric acid cannot irritate it as easily.  This is another very safe, easy-to-use medication that also happens to work well for diarrhea.  


***Although you can technically take both of these at the same time, it’s typically not needed.


Vertigo is defined as the feeling of a sense that your environment is spinning.  Motion sickness slightly different in that it is a feeling of being “off-balance” following repetitive motion like a boat or car ride.  Nonetheless, both of these are dysfunctions of the vestibular system, which as we discussed earlier, can certainly cause nausea.

Since vestibular system dysfunctions are communication via Histamine 1 receptors, the best medications to use are antihistamines, specifically H1 antagonists.  The two that we have to choose from are Diphenhydramine and Meclizine.

Diphenhydramine (Benadryl)

Works by competitively binding to histamine 1 receptors to prevent histamine from sending messages to the vomiting center.  Overall, diphenhydramine works well for this.  However, it tends to make the patient very drowsy.  You may have heard of a brand name drug called Dramamine.  This is essentially diphenhydramine mixed with a stimulant called 8-chlorotheophylline to make Dimenhydrinate.  This allows the patient to have the same therapeutic effects, without the drowsiness.  

Meclizine (Antivert)

Meclizine also functions on histamine 1 receptors and is found to be a “non-drowsy” alternative to diphenhydramine.  Not officially a drug in our scope of practice, but a useful over-the-counter medication indeed!

If nausea or vomiting is prolonged or it doesn’t have a clear causative source, then it’s time to bring out the big guns: Ondansetron and Promethazine.

Ondansetron (Zofran)

Originally designed to prevent nausea for patients undergoing chemotherapy, Ondansetron has become a very popular option for safe, effective nausea control.  It works specifically on serotonin receptors (5-HT3) in the brain.  Although it’s very effective for patients with nausea, it doesn’t appear to be overly effective for patients experiencing active episodes of vomiting. 

Promethazine (Phenergan)

For more immediate control of active vomiting, promethazine is the way to go.  Primarily acts on histamine 1 receptors, but also has some effect on dulling the CTZ of the medulla.  In addition, it exerts mild inhibition on serotonin receptors.  So as you can see, this works on several nausea/vomiting pathways.  The tricky thing about promethazine though is that it’s heavily sedating and makes patients feel groggy.  Anybody receiving this medication should be considered out of the fight for the day.    

Excessive vomiting can cause patients to become severely dehydrated.  Naturally, PO hydration will probably be out of the equation.  IV fluids may be required.


Remember, nausea/vomiting by itself doesn’t necessarily require an evacuation plan…. but the underlying condition causing it may require it. Always be sure to work up all these patients and get a solid history.

Good luck out there!



  • Putra OD, Yoshida T, Umeda D, Higashi K, Uekusa H, Yonemochi E (29 July 2016). “Crystal Structure Determination of Dimenhydrinate after More than 60 Years: Solving Salt–Cocrystal Ambiguity via Solid-State Characterizations and Solubility Study”. Crystal Growth & Design16 (9): 5223–5229.
  • Miloro, ed. by Michael (2012). Peterson’s principles of oral and maxillofacial surgery (3rd ed.). Shelton, CT: People’s Medical Pub. House-USA. p. 86. ISBN 978-1-60795-111-7Archived from the original on 2016-02-01.
  • Talley NJ, Vakil N (October 2005). “Guidelines for the management of dyspepsia”. Am. J. Gastroenterol100 (10): 2324–37. doi:10.1111/j.1572-0241.2005.00225.xPMID 16181387.
  • Advanced Tactical Paramedic Protocols Handbook. 10th ed., Breakaway Media LLC, 2016.
Brandon Simpson, PA-C
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