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Weight Loss

15 min read

Are weight loss pills safe? What you need to know.

Written by Brittney Bertagna

Published: Jan 12, 2024

Medically Reviewed by Dr. Kasra Tayebi

Table of contents

Americans like the idea of using a pill for weight loss. In fact, some 45% of Americans want prescription weight-loss drugs. But are weight loss pills safe?

Here, we look at popular weight loss medications and their risks to give you answers. 

Prescription vs OTC weight loss pills

When it comes to weight loss pills, there are three categories: prescription, over-the-counter (OTC), and supplements. 

Prescription medications require a doctor’s approval. They’re clinically tested for safety and efficacy and approved for specific use by the U.S. Food and Drug Administration (FDA). 

Talk to a provider online about a weight loss prescription within 24 hours.

Over-the-counter weight loss pills are available without a prescription. These types of medications are regulated by the FDA for safety when used as indicated and directed. 

Supplements, like herbal remedies, are available over-the-counter but aren’t regulated by the FDA. Meaning there’s no guarantee of a dietary supplement’s safety or efficacy.

Regardless of the type of medication, it’s important to consult with a healthcare provider before taking any weight loss pills to ensure they’re safe for you.

How do you know which weight loss pills are safe? 

Ways to gauge the safety of a weight loss pill include looking it up in the database of FDA-Approved Drugs, talking to your doctor, talking to your pharmacist, and reading the medication’s drug guide, which is available online or from your pharmacist. 

FDA-approved pills undergo rigorous testing and meet specific criteria for efficacy, safety, and manufacturing standards. 

For dietary supplements, look for third-party approvals, like the NSF International supplement and vitamin certification, talk to your doctor, and carefully read labels for potential risks or interactions with medications. 

Are prescription weight loss pills safe?

To determine if prescription weight loss pills are safe for you, consult a healthcare professional. Your provider will take into account your medical history and assess your current physical health to determine the safest and most effective weight loss program for you.

While prescription weight loss pills can be effective, they also have potential side effects. Common side effects include gastrointestinal symptoms, such as diarrhea and abdominal pain, and changes in blood pressure and heart rate. These side effects are typically mild and temporary but vary depending on the specific medication and individual health status.

Here’s a rundown of what you need to know about the safety and potential side effects of some of the most popular prescription weight loss medications available today.

Note: Before taking any medication, talk to your doctor and be aware of potential side effects by reading the medication guide provided by your pharmacist and linked below.

Discover a tailored approach to weight loss that fits your unique needs.

Zepbound and Mounjaro (tirzepatide)

Tirzepatide is the active ingredient in two brands of medication: Zepbound and Mounjaro. Tirzepatide activates receptors of certain hormones in the intestine called glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide, which helps reduce appetite and food intake and contribute to weight loss. 

Zepbound is approved by the FDA for chronic weight management. Mounjaro is the same medication sold under a different name and approved to lower A1C in type 2 diabetics when combined with diet and exercise.

Tirzepatide is considered safe for most people. It shouldn’t be used with any other GLP-1 receptor agonist. And, as with any medication, there are potential risks and side effects. 

The most common side effects of tirzepatide include gastrointestinal distress, such as nausea, diarrhea, vomiting, constipation, abdominal discomfort, injection site reactions, fatigue, and hypersensitivity responses, such as fever or rash.

Serious risks associated with tirzepatide include a risk of severe hypoglycemia (low blood sugar). Additionally, an increased risk of developing pancreatitis is associated with tirzepatide. Those with a history of kidney problems should be monitored closely. 

The FDA issued a black box warning, the highest level of warning the FDA issues for medications, about the potential risk of thyroid cancer. It’s important to note that this warning is based on animal studies, and no human trials have found a link between tirzepatide and thyroid cancer. It’s advised, though, that those with a history or family history of medullary thyroid cancer or endocrine neoplasia syndrome type 2 avoid taking tirzepatide.

Wegovy and Ozempic (semaglutide)

Semaglutide is a medication used for chronic weight management in adults with obesity or who are overweight. It’s the active ingredient in both Wegovy and Ozempic, which are taken as a once-weekly injection. Semaglutide works by mimicking the action of GLP-1, which helps regulate blood sugar levels.

While semaglutide is considered safe for use in most people, there are risks associated with its use. Semaglutide has the same black box warning for thyroid cancer as tirzepatide. 

The FDA also issued a warning about the possibility of intestinal blockages when taking Ozempic or Wegovy.


Wegovy is FDA-approved for chronic weight management in adults with obesity or who are overweight and have at least one weight-related condition, such as hypertension or type 2 diabetes. 

Wegovy is considered safe for use when used as directed. Common side effects include stomach pain or upset, heartburn, headache, fatigue, dizziness, bloating, belching, and gas. 

Serious side effects that have occurred in up to 6% of patients include pancreatitis, gallbladder disease, hypoglycemia (low blood sugar), kidney injury, allergic reactions, diabetic retinopathy, increased heart rate, and suicidal behavior.

Wegovy should be used with caution in people with kidney, pancreas, or vision disorders.

Wegovy hasn’t been studied in patients with pancreatitis or severe gastroparesis. Therefore, it’s not recommended for use in these individuals. 


Ozempic has FDA approval for the treatment of type 2 diabetes. 

Ozempic is generally considered safe when taken as prescribed. Common side effects of Ozempic include nausea, vomiting, diarrhea, and decreased appetite. 

Those with a history of kidney problems should be monitored closely.

While not FDA-approved for the treatment of chronic weight management, Ozempic has gained recent popularity for unapproved or off-label use for medication-assisted weight loss. 

Saxenda (liraglutide)

Saxenda is an injectable medication with liraglutide as the active ingredient. It mimics GLP-1, which helps regulate appetite. Saxenda has FDA approval for weight management in adults with obesity or overweight individuals with at least one weight-related medical condition. It’s considered safe for most people. 

Common side effects of Saxenda include nausea, diarrhea, and low blood sugar. More severe side effects are possible, such as pancreatitis, thyroid tumors, and allergic reactions.

While studied for safety, adults, children, adolescents aged 12 to 17, and those who have a history of pancreatitis or thyroid disease should use precautions if taking Saxenda.

Contrave (bupropion-naltrexone)

Contrave is an oral medication used for weight management. It combines two active ingredients, bupropion and naltrexone.

Common side effects of Contrave include nausea, vomiting, dizziness, dry mouth, constipation and headache. 

More serious side effects include increased blood pressure, a risk of seizures, and thoughts of suicide. For this reason, Contrave isn’t suitable for everyone, especially those with uncontrolled high blood pressure, seizure disorders, or a history of eating disorders, as well as individuals who are pregnant or breastfeeding. 

Talk with your doctor or a therapist if you experience depression or thoughts of harming yourself or others while on Contrave.

Xenical and Alli (orlistat)

Orlistat is an active ingredient in two medications used for weight loss: Xenical (orlistat 120 mg), available by prescription, and Alli (orlistat 60 mg), available over the counter. Orlistat decreases the amount of fat absorbed by the intestines.

Common side effects of orlistat include fecal spotting, gas, increased fecal urgency, fatty or oily stools, and increased frequency of bowel movements. These side effects are usually mild and temporary.

There are rare reports of severe liver injury on orlistat, which led to the addition of an FDA warning label to the medication. Symptoms of liver injury include itching, yellow eyes or skin, dark urine, loss of appetite, or light-colored stools. If you experience any of these symptoms, contact your healthcare professional immediately.

Avoid orlistat if you’ve had an organ transplant. 

Qsymia (phentermine-topiramate)

Qsymia is an oral prescription weight loss pill. The active ingredients in Qsymia are phentermine and topiramate. Phentermine mimics neurotransmitters in the brain to reduce hunger. Topiramate affects other neurotransmitters to reduce appetite and increase feelings of fullness.

Common side effects when taking Qsymia include dizziness, drowsiness, dry mouth, trouble sleeping, tingling in the hands/feet, joint aches, constipation, and a metallic taste in your mouth. 

More serious side effects can include difficulty concentrating or remembering things, kidney stones, rapid breathing, changes in heartbeat, bone pain, passing out, and unusual bleeding/bruising. If you’re taking Qsymia and notice any sudden changes in mood or sleep, such as insomnia, or side effects persist, consult your doctor, pharmacist, or a specialist.

Qsymia can cause birth defects. For this reason, it’s advised to consult your doctor before using it if you’re pregnant or are trying to become pregnant. 

Rely on medically supervised weight loss for maximum safety 

To ensure your safety and well-being on any medically supervised weight loss journey, it’s important to consult a healthcare professional who knows your medical history and status and can monitor you throughout the process. 

With Klarity, discover a medication-managed approach to weight loss with medical weight-loss professionals who can help you with your weight loss journey. Find a provider on Klarity and start today. 

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