The body signals to stop: Weight-loss injections have become one of the greatest revolutions in modern medicine, but for quite a few patients, the path to a lower weight passes through nausea, vomiting, diarrhea, belching, abdominal pain, and a feeling of fullness that arrives too quickly. These phenomena are not rare, and in most cases, they are directly related to the drug's mechanism of action. The good news is that in a large portion of cases, they can be reduced through dietary adjustments, adequate hydration, a slower dosage increase, and sometimes short-term medical treatment under medical supervision.
Wegovy and Mounjaro, the two main medications currently sold in Israel for obesity management, act on a hormonal system that regulates hunger, satiety, sugar, and digestion. Wegovy contains semaglutide, a drug that mimics the activity of the GLP–1 hormone. Mounjaro contains tirzepatide, which acts on two hormonal pathways, GLP–1 and GIP. Both drugs are administered via a subcutaneous injection once a week, and they cause the brain and digestive system to receive a clearer message of satiety.
Data from large studies explain why the enthusiasm for these drugs is so great. In a major study published in the medical journal New England Journal of Medicine, treatment with semaglutide at a dosage of 2.4 mg once a week, alongside lifestyle modification, led to an average weight loss of 14.9% after 68 weeks, compared to 2.4% in the placebo group. In another large study in the same journal, treatment with tirzepatide led to an average weight loss of up to 20.9% after 72 weeks at the highest dosage tested. In simple terms, these are results that were previously closer to the world of bariatric surgery than to conventional medical treatment.
But the very same action that assists in weight loss is also the one that can cause discomfort. The medications slow down gastric emptying. Food remains in it for a longer duration, satiety arrives faster, and the body reacts intensely to large or fatty meals. A person who was used to eating a large plate quickly may find that under the treatment, the same amount no longer suits them. The stomach is full, its movement is slower, the brain receives a message of satiety, and if the patient continues to eat beyond this point, nausea and sometimes vomiting may occur.
Therefore, vomiting is not necessarily a sign that the medication is "unsuitable", but rather sometimes a sign that eating habits have not yet changed at the pace at which the medication has already started working. Those who continue to eat quickly, finish every portion on the plate, drink carbonated beverages during the meal, or choose fried and fatty food, increase the risk of nausea and a sensation of overload. The medication essentially obligates the patient to relearn the language of satiety: To stop early, eat slowly, and understand that a small portion can suffice.
Diarrhea is also a known side effect of these medications. The explanation is more complex than that for vomiting, but it is related to the effect of the drugs on the motility of the digestive tract, fluid secretion in the intestine, intestinal sensitivity, and the rapid change in eating habits. Some patients switch abruptly to a menu rich in vegetables, proteins, sugar substitutes, nutritional supplements, or diet foods, and the intestine responds accordingly. For others, fatty or spicy food, large amounts of coffee, alcohol, or artificial sweeteners may exacerbate loose stools and urgency.
In this sense, side effects sometimes also have an "educational effect". They force the patient to do what is recommended anyway in obesity treatment: To eat less, slower, more orderly, and healthier. But it is important to state clearly: One does not need to suffer to lose weight. Repeated vomiting or significant diarrhea is not a necessary part of the treatment, and they require adjustment.
The first step is reducing portions. Instead of three large meals, it is preferable to switch to several small meals throughout the day. Sometimes half a sandwich, yogurt, an egg, soup, fish, chicken, cooked vegetables, or a small portion of rice will digest better than a large meal. It is advisable to eat slowly, pause between bites, and stop at the first sign of satiety. Not when there is pain, not when there is nausea, but already at the stage where the body signals that it is enough.
The second step is choosing food that is easier to digest. During a period of nausea or diarrhea, fried food, fatty meat, heavy sauces, pastries rich in butter, cream, high-fat cheeses, carbonated beverages, and alcohol should be avoided. It is better to choose simpler foods: Rice, potatoes, banana, toast, clear broth, chicken, fish, eggs, and cooked vegetables. For those suffering from diarrhea, a temporary reduction in coffee, spicy food, artificial sweeteners, and dairy products may also help.
The third step is hydration. Vomiting and diarrhea can cause a loss of fluids and salts, and in severe cases, even kidney injury, especially in patients with underlying medical conditions, older adults, or those taking diuretics. It is important to drink in small sips throughout the day. When experiencing nausea, drinking a large glass rapidly can worsen it. In cases of significant diarrhea, an oral rehydration solution can be considered, especially if there is weakness, dizziness, or decreased urination.
For diarrhea, one can also sometimes use products such as Tasectan, in accordance with the recommendation of a physician or pharmacist. The active ingredient in the product is gelatin tannate, which acts locally in the intestine and is designed to create a sort of protective layer on the intestinal mucosa. The purpose is to reduce local irritation, assist in restoring the function of the intestinal wall, and reduce the frequency and wateriness of bowel movements. However, Tasectan does not replace a medical evaluation if there is a fever, blood in the stool, severe abdominal pain, prolonged diarrhea, or signs of dehydration.
One of the most important points is the rate of dosage titration. Side effects frequently appear at the beginning of treatment or after switching to a higher dosage. In sensitive patients, it is possible to consider, together with the doctor, staying longer at a lower dosage, delaying an increase, temporarily down-titrating to a previous dosage, or ascending more slowly. One must not increase the dosage independently to "speed up" weight loss, and treatment must not be stopped without consultation, especially in diabetic patients or patients with underlying illnesses.
In cases of significant nausea or vomiting, a physician may consider temporary treatment with anti-nausea and anti-vomiting medications, such as Pramin or Motilium. Here, caution is required: Pramin can cause side effects in the nervous system, and Motilium can be problematic for some patients due to a potential effect on heart rhythm and interactions with other drugs. Therefore, they should not be viewed as an automatic solution, but rather as a targeted treatment under medical consultation.
There are situations in which one must not make do with dietary tips: Repeated vomiting that prevents drinking, prolonged diarrhea, decreased urination, severe dizziness, unusual weakness, high fever, blood in the stool, severe abdominal pain, or pain that radiates to the back. Unusual abdominal pain under these medications also requires examination, among other things, to rule out rare but important conditions such as pancreatitis, gallbladder problems, bowel obstruction, or significant dehydration.
Weight-loss injections are not magic that allows one to continue eating as in the past. They alter the sensation of hunger and satiety, slow down the stomach, and require a new attentiveness to the body. Those who understand this early, reduce portions, eat slowly, drink correctly, and consult with the doctor before any dosage change, increase the chance of enjoying the great benefits of the treatment without paying a heavy price in the digestive system.
Dr. Itay Gal is a specialist in pediatrics, a sports and aviation physician, and the medical commentator for Maariv. For more articles click here