As with any medication, there is no way to predict who will or won’t experience side effects. Despite the side effects of the medication, Jastreboff insists on The Medical Necessity of Treating Obesity. The author acknowledges that many people who use obesity medications experience gastrointestinal side effects of vomiting, diarrhea, constipation, and nausea. For instance, 30-45% experience nausea, the most common side effect, at some point in the first year. Not everyone experiences these, however, and they do tend to subside over time. Jastreboff explains that these side effects are more common when the dosage is administered or increased. With this in mind, patients can plan their dosages around their calendars, making sure they feel their best when they need to.

While patients in a research trial have to use the prescribed dose at certain times, others can increase their dosage incrementally. She advises readers to “[s]tart low, go slow” to avoid these side effects (209). Other tips are to eat slowly to allow the body to register a feeling of fullness and to eat small, frequent, and healthy meals. Hydrating is also essential. Patients have varying experiences on these medications. Some patients are energized, while others are fatigued. Rapid weight loss can cause hair loss, but this typically goes away after weight has plateaued. If it persists, a dermatologist could recommend treatment. Since new medications are prompting huge weight loss, their risks are similar to those of gastric bypass surgery, such as decreasing bone density and vitamin deficiencies. The author’s description of these side effects presents them as potentially serious but not inevitable. 

Jastreboff blames irregular dosing for exacerbating certain side effects. She points to the example of Todd, a teacher in his late thirties. He took a break from his medications while on vacation, wanting to enjoy the all-you-can-eat buffets he had paid for at the all-inclusive resort. Upon returning home, he felt normal and thought he might not need his medications anymore. Once the dosage wore off, he began to experience cravings again and overate. Feeling bad, Todd took the usual dosage again and experienced terrible vomiting requiring hospitalization. His doctor explained that his body needed to acclimatize to the medications since he had taken a break, and they started Todd on the lowest dosage again. This anecdote illustrates how using the medications consistently and as prescribed is crucial for avoiding the worst of their potential side effects, but Jastreboff keeps the focus on largely positive anecdotes.

In a rarer example of side effects, a woman named Qisha had inflammation of the gallbladder and needed it removed. Gallbladder inflammation and gallstones are a rare but possible side effect of every kind of rapid weight-loss treatment. Pancreatitis is another rare side effect. Jastreboff advises that patients seek emergency help if they have abdominal pain while using the medications. She also notes that if patients have a family history of medullary thyroid cancer or multiple endocrine neoplasia, their doctors may not prescribe them the medication. 

Jastreboff reiterates that while the medications have potential side effects, there are also risks to not treating obesity, including serious illnesses such as heart disease, kidney disease, and cancer. She recommends that doctors and patients evaluate all risks together to make an informed decision about whether or not to try these medications and urges readers to always honestly discuss side effects with their doctors.