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What Are The Side Effects Of Weight Loss Medications?

May 23, 2022
What Are The Side Effects Of Weight Loss Medications?

Obesity is a chronic disease that affects approximately 42% of U.S. adults. Like high blood pressure, it silently causes damage to blood vessels and strains the heart. It also increases your risk of developing type 2 diabetes.

One difference between high blood pressure and obesity is that there are a lot of myths and stereotypes about obesity. Obesity is a complex disease. It’s not just a result of overeating or being lazy. Weight gain is more than just calculating calories in and calories out. Short-term weight loss may be achieved through restrictive diets and excessive exercise, but approximately 90% of people who lose a significant amount of weight will gain it back.

Obesity raises your risk of developing other serious diseases, reduces your quality of life, and shortens your life span.

Whatever your health goals, there are prescription and non-prescription medications to help with weight loss, as well as medically supervised weight loss treatment plans. These treatment options are meant to be used in conjunction with a healthy diet and exercise routine.

It’s critical to be aware of all of your weight-loss medication and treatment options. There are many more options than there were just a decade ago, whether you prefer weight loss injections, lipotropic injections, or prescription pills to treat weight loss.

Drugs For Chronic Weight Management

Prescription weight loss medications are recommended for people with obesity, defined as a BMI of 30 or higher, or people with a BMI of 27 or higher who have a co-existing serious medical problem that is related to obesity, such as type 2 diabetes or high blood pressure.

There are four main classes of prescription medications used to treat obesity:

  • Medications that increase chemicals in your brain, so you feel full. Examples include phentermine, a combination of phentermine and topiramate, or a combination of naltrexone and bupropion.
  • Medications like orlistat interfere with fat absorption by blocking lipase, an enzyme that breaks down fat. As a result, approximately one-third of the fat you eat passes through the intestines to be expelled as waste.
  • Glucagon-like peptide-1 (GLP-1) agonists target areas of the brain that regulate appetite and food intake. Examples include liraglutide and semaglutide.

Doctors and patients work together to determine weight loss goals. Then they consider side-effect profiles, the amount of weight loss needed versus the amount the medication is likely to cause, and the medication cost to determine the best choice for each person.

weight loss treatment


When weight loss medications are used correctly along with a healthy diet and exercise program, they can boost weight loss, with some causing 5% to 10% or more body weight loss.

Side Effects

Like all medications, weight loss medications have side effects. In most cases, side effects improve as your body adapts to the medications. If side effects don’t get better or get worse, medications can be stopped, or the dose can be changed. Talk to your doctor before changing your medication regime.

This list of commonly prescribed weight-loss medications and their side effects is not meant to be all-inclusive. Talk to your doctor about any side effects you might experience.

Medications That Reduce Appetite:

Phentermine is a stimulant medication.

  • It cannot be used if you have heart disease, uncontrolled high blood pressure, hyperthyroidism, or glaucoma.
  • Side effects
    • Constipation
    • Insomnia
    • Nervousness and irritability
    • Headache

Phentermine/Topiramate is a combination stimulant and anti-seizure medication.

  • Do not use if you have glaucoma, heart disease, or hyperthyroidism.
  • Side effects
    • Constipation
    • Dizziness
    • Dry mouth
    • Changes in the sense of taste
    • Tingling in hands and feet
    • Insomnia

Bupropion/Naltrexone is a combination antidepressant and medication that blocks opioid receptors. It blunts the response from the reward system in the brain after eating highly palatable foods.

  • Do not use it if you have high blood pressure, anorexia, or seizures. Do not take this medicine if you are dependent on an opioid medication or are withdrawing from drugs or alcohol.
  • Side effects    
    • Constipation
    • Diarrhea
    • Dizziness
    • Increased blood pressure and heart rate
    • Nausea and vomiting
    • Headache

Medications That Block Fat Absorption:

Orlistat blocks the absorption of fat.

  • Take it with a multivitamin to increase fat-soluble vitamins.
  • Side effects
    • Diarrhea
    • Oily discharge
    • Gas
    • Stomach pains

Medications That Affect Carbohydrate Metabolism:

Liraglutide and semaglutide mimic the action of GLP-1 by modulating appetite and slowing stomach emptying to reduce food intake.

  • May increase the risk of pancreatitis and a rare type of thyroid cancer (only in animal studies).
  • Side effects
    • Nausea
    • Diarrhea
    • Constipation
    • Headache
    • Fast heart rate

Metformin is used to treat type 2 diabetes and is used off label for weight loss.

  • May cause lactic acidosis.
  • Side effects
    • Stomachache
    • Diarrhea
    • Nausea
    • Vomiting
    • Gas

Other Treatments For Weight Loss

There are non-approved medications that people use for weight loss. These medications are used off-label, which means that your doctor has determined that the benefits of the medication exceed the risk of taking them. These medications may be prescribed for anyone who wants to lose excess weight or change their body composition by increasing muscle mass and reducing fat mass.

Hormonal Treatments

Hormones are proteins in the body that are secreted by one body organ and have effects on other body organs.


Oxytocin is a small six amino-acid peptide used for decades to control uterine contractions. Almost 400 completed, ongoing, or future-funded clinical trials have tested or are designed to test oxytocin’s ability to reduce cravings, especially for fatty foods.

Oxytocin benefits

  • Reduces hunger.
  • Reduces cravings.
  • Increases energy expenditure.
  • Increases fat breakdown.

Oxytocin side effects

  • Nausea
  • Vomiting
  • Stomachache
  • Runny nose and congestion
What Are The Side Effects Of Weight Loss Medications?


Testosterone is an anabolic-androgenic hormone that increases muscle mass and reduces fat mass in men who have testosterone deficiency.

Testosterone benefits

  • Regulates carbohydrate, protein, and fat metabolism.
  • Increases muscle growth.
  • Increases motivation and physical activity.
  • Reduces fatigue.
  • Improves mood.

Testosterone side effects

  • Increased risk of blood clots
  • Mood changes
  • Urinary symptoms
  • Back pain
  • Fluid retention
  • Acne
  • Gynecomastia
  • Sleep apnea


Sermorelin is a weight loss injection that stimulates the release of growth hormone. It stimulates natural growth hormone release; it is not growth hormone replacement. Human growth hormone declines, starting around age 30.

Sermorelin benefits

  • Decreased abdominal fat
  • Increased muscle mass
  • Increased bone mass
  • Improved strength
  • More energy

Sermorelin side effects

  • Pain or redness at the injection site
  • Dizziness
  • Flushing
  • Headaches

Lipotropic Nutrients

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Lipotropics are vitamins and other nutrients that help your body mobilize fat and use it for energy, promoting weight loss. Lipotropics help move fat from the liver to be burned as a source of energy. These nutrients can be delivered as weight loss lipotropic injections or pills.


Methionine is an essential amino acid that acts as an antioxidant to neutralize harmful chemicals and molecules in the body.


Inositol is a naturally occurring sugar that plays a role in cell structure, metabolism, energy storage, energy consumption, and stress response. As a result, inositol increases weight loss and reduces fat mass. It may also decrease insulin resistance, which can improve glucose utilization.


Choline is important in generating energy. It moves fat and bile from the liver so it can be used as a source of energy.

lipotropics and nutrients

Vitamins And Other Supplements

Vitamins and other supplements can support energy, making it easier to exercise. Since these vitamins and nutrients are found in the diet and in the body, they rarely cause side effects unless taken in extremely large doses.

Vitamin B12

Vitamin B12 is a key cofactor in many chemical reactions in the body, especially ones involved in fat and carbohydrate metabolism. Researchers have found that people with low B12 levels are at an increased risk of being overweight or obese.


Glutathione is a powerful antioxidant. Poor nutrition and exposure to environmental stresses affect glutathione levels. Increasing glutathione levels can help your liver work better and use glucose more efficiently.


Carnitines transport fatty acids into the mitochondria, where they can be burned for energy. Carnitine also plays a role in carbohydrate metabolism.

The Bottom Line

Weight-loss medications today are safer and more effective than options even a decade ago. All medications have side effects and should not be used in people with known contraindications. Clinical trials, including cardiovascular outcome trials, have shown that weight loss drugs approved are safe and effective.

Most medications that are used off-label for weight loss have also undergone testing, but it may have been for another disease indication, and weight loss was a side effect.

These medications require a consultation with a medical professional and a prescription. This is to evaluate whether you have any contraindications to the medications and to determine whether the known risks outweigh the benefits. If you need help managing your weight, consult with a doctor to learn whether one of these medications is right for you.

Start a weight management treatment plan today!

While we strive to always provide accurate, current, and safe advice in all of our articles and guides, it’s important to stress that they are no substitute for medical advice from a doctor or healthcare provider. You should always consult a practicing professional who can diagnose your specific case. The content we’ve included in this guide is merely meant to be informational and does not constitute medical advice.

What Are The Side Effects Of Weight Loss Medications?

Leann Poston, M.D.

Dr. Leann Poston is a licensed physician in the state of Ohio who holds an M.B.A. and an M. Ed. She is a full-time medical communications writer and educator who writes and researches for Invigor Medical. Dr. Poston lives in the Midwest with her family. She enjoys traveling and hiking. She is an avid technology aficionado and loves trying new things.


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