5 Side Effects of Diet Pills You Can Experience

Dr. Harshi Dhingra, MBBS, MD
Published by Dr. Harshi Dhingra, MBBS, MD | Medical Doctor
Last updated: June 22, 2024
FACT CHECKED by Dr. Kristy Dayanan, BS, MD
Our content is meticulously researched and reviewed by an expert team of fact checkers and medical professionals. They ensure accuracy, relevance, and timeliness using the latest reputable sources, which are cited within the text and listed at the end of the article. Before publication and upon significant updates, we confirm factual accuracy, committed to providing readers with well-informed content. Learn more.

From a medical perspective, it's important to acknowledge that combining a restricted diet with exercise and specific fat burners can accelerate weight loss and combat obesity. However, it's crucial to understand the complete picture.

As a doctor, I must caution that certain ingredient combinations commonly found in fat-burning supplements can lead to dangerous side effects.

No one should have to face such risks in pursuit of rapid weight loss.

In our commitment to patient safety, we have reviewed pertinent medical literature and consulted with fellow experts. Our goal is to inform you about the scientifically validated adverse reactions associated with certain substances marketed for weight loss. We also provide guidance on how to avoid these risks.

Quick Summary

  • Common side effects of fat burners include dehydration, headaches, insomnia, increased heart rate, and liver damage.
  • To effectively manage weight loss, it's crucial to understand that fat burners can accelerate the process but may cause serious side effects.
  • According to the National Instute of Health, high doses of stimulants such as Caffeine, Yohimbine, and Bitter Orange can dehydrate you, causing headaches and migraines.
  • In my view, while fat burners can aid in weight loss, adopting a healthy lifestyle with diet and exercise is a safer and more sustainable approach.

What Are the Side Effects of Fat Burners?

woman seated on the floor puking in a toilet bowl, and a man holding his temples in pain

The typical side effects most people who used fat-burning supplements have reported are mild reactions like:

  • Dry mouth 
  • Unpleasant taste 
  • Acne
  • Itchiness 
  • Allergies 
  • Jitters   
  • Hot flushes 
  • Nausea
  • Vomiting
  • Diarrhea, gas passing, and other stomach issues    
  • Nervousness  
  • Dizziness  
  • Tremor  
  • Confusion  
  • Blurred vision and similar

As a physician, I advise patients to understand that the effectiveness of fat burner supplements in weight loss can differ from person to person.

While certain individuals might find these supplements beneficial in their weight loss endeavors, others may not see similar results.

It's important to recognize that a fat burner is not a miraculous cure; it should be viewed as an adjunct to a well-rounded approach that includes a balanced diet and consistent exercise.

Below, I have compiled a comprehensive list of the most prevalent side effects, as identified by scientific research, along with various ingredients commonly found in fat burners that are associated with each of these side effects.

1. Dehydration and Headache

man holding his head in pain, and a woman tired holding a water bottle

According to the National Instute of Health (NIH), apart from banned drugs like Phentermine and Ephedrine, high doses of stimulants such as Caffeine, Yohimbine, and Bitter Orange can dehydrate you, causing headaches and migraines [1].

This dehydration, worsened by not drinking enough water and intense exercise, especially in hot weather, can trigger other physical and mental health problems, such as:

  • Skin problems
  • Constipation and other stomach issues
  • Impaired memory functions
  • Anxiety
  • Kidney complications, etc.

They can also greatly impact your social, work, and emotional life.

2. Insomnia

woman covering her ears with pillows in frustration

Some stimulative compounds found in fat burners can change your sleep patterns and cause sleeplessness, resulting in sleep deprivation.

Lack of sleep and rest may jeopardize your immune system, metabolism, and other body functions, negatively influencing your overall emotional, physical, and mental health.

3. Increased Heart Rate, Blood Pressure Fluctuations, and Other Heart Complications

aged man with both of his hands in his chest in pain

Research from NIH indicates that thermogenic ingredients in fat burners, aimed at enhancing fat metabolism and reducing hunger, are associated with high blood pressure, irregular heartbeats, strokes, and other heart-related problems, particularly in unhealthy obese individuals [2].

Stimulants like Caffeine, Green Tea extract, Yohimbe, Ephedrine, Fenfluramine, and PPA have been shown by research from the National Library of Medicine to increase blood pressure and heart rate [3].

“Like ephedra, synephrine may speed up your heart rate and raise your blood pressure. Strokes and heart attacks have been reported in some people after taking bitter orange alone or in with other stimulants such as caffeine.”

- Brent A. Bauer, M.D., Mayo Clinic

The National Institutes of Health and another journal have found that Citrus Aurantium may interact with Synephrine, constricting your blood vessels and causing BP fluctuations, even a heart attack [4] [5].

Related Article: Can You Take Fat Burners With High Blood Pressure?

4. Psychological Side Effects

woman covering her face while crying

As a doctor, I want to highlight that ingredients in fat burners like Ephedrine and Yohimbine stimulate the central nervous system, boosting fat burning and reducing fat absorption, which helps in weight loss.

They also make you feel fuller and curb hunger by affecting brain chemicals and cortisol levels.

But, this overstimulation can cause behavioral changes, including irritability, anxiety, mood swings, and even suicidal thoughts.

So, I strongly recommend consulting a healthcare professional before using these supplements.

5. Liver Damage

man holding his right waist in pain

Research from NIH shows that long-term use of fat burners with usnic acid, Green Tea, and Guggul tree extracts can cause severe liver toxicity, potentially leading to acute liver failure, transplant needs, or even death [6].

Symptoms include fatigue, nausea, vomiting, jaundice, and abdominal pain. Chromium polynicotinate, often in fat burners, and Kombucha tea, with usnic acid, can harm the liver.

Aegeline, from the Indian Marmelos Correa plant, also causes liver inflammation and similar issues.

Other fat burner ingredients, interacting with heavy metals and plant extracts like Garcinia Cambogia, may damage the liver.


Fat-burning pills can interact with common foods and drinks. Caffeine, often present in pills, may amplify its stimulant effects.

Alcohol might hinder fat metabolism and intensify side effects.

Certain diets, especially high-fat or low-carb, can influence how the body processes fat burners, affecting effectiveness and potential side effects.

How to Get Rid of Fat Burner Side Effects and Lose Weight Safely

woman chugging a bottle of water, and a man holding up a weighing scale while flexing his arms

As a medical professional, I advise that the most reliable and effective method for fat loss and maintaining a healthy weight over the long term is a combination of a clean, calorie-controlled diet and regular physical activity.

In essence, adopting a healthy lifestyle is preferable to seeking quick fixes for fat loss.

However, if you find yourself needing to use fat burners to manage excess body weight, it's crucial to take steps to mitigate potential side effects. As always, consulting with a healthcare provider is recommended for personalized advice and safety.

Stay Hydrated

For instance, increasing your water intake can keep dehydration, headache, constipation, cognitive issues, and other common side effects that accompany dehydration at bay.

Keep an Eye on Caffeine and Other Stimulants Consumption

woman avoiding a coffee cup

Not taking fat burners high in Caffeine and other stimulants that may keep you up at night within five hours of bedtime can help you avoid insomnia.

Also, limit your daily Caffeine consumption from coffee, tea, guarana, and other energy drinks and foods to minimize the risk of hypertension, heart palpitations, and heart attacks.

Mind the Dosage

As a doctor, I recommend selecting stimulant-free supplements with lower dosages and steering clear of products containing banned or harmful ingredients that might interact negatively with your medications and impact your health.

It's particularly important for pregnant or breastfeeding women, individuals with diabetes, cardiovascular conditions, anorexia, or other chronic diseases, to avoid weight loss supplements.

I also advise that even healthy people should seek advice from a healthcare professional before beginning any supplement regimen.

Comparison with Natural Fat-Burning Methods

Fat-burning pills and natural methods like diet and exercise differ significantly. Pills may offer quicker results, but their efficacy varies, and long-term effects remain uncertain.

Natural methods, emphasizing a balanced diet and regular exercise, are more sustainable and promote overall health.

While pills may cause side effects like insomnia or digestive issues, natural approaches generally have fewer adverse effects. Results from pills might appear faster, but lifestyle changes yield gradual but more enduring outcomes.


Can Weight Loss Pills Cause Hair Loss?

Although high-quality weight loss supplements have rarely been linked to this issue, Phentermine is a weight loss medication that can cause hair loss.

Some other fat burner ingredients may also significantly raise your cortisol level and a male sex hormone dihydrotestosterone (DHT), sometimes leading to excessive hair thinning or loss.

Learn more: Can Fat Burners Cause Hair Loss?

Can Fat Burners Affect Fertility?

Some stimulants and plant-based compounds in fat burner supplements, as well as nutrient deficiency, starvation, and rapid weight loss, can affect fertility.

Learn more: Can Fat Burners Affect Fertility?

Can Fat Burners Mess With Your Period?

Yes, certain fat burners can mess with your period directly (containing potent stimulants and other ingredients that affect your hormones, e.g., increase cortisol and DHT) or indirectly (causing rapid weight loss and body fat percentage reduction).

Learn more: Can Fat Burners Affect Your Period?

Are Fat Burner Pills Dangerous?

Although many of them are safe, some fat burner pills can be dangerous as they don’t need to be regulated by the Food and Drug Administration (FDA). So, they might contain some banned, unsafe, and ineffective chemicals, causing serious side effects like strokes, seizures, even death.

For your safety, it’s critical to seek professional medical advice from your healthcare provider and do thorough research before purchase to know what exactly your chosen supplement contains, ensure it’s top-quality, and stick to the manufacturer’s dosage and other recommendations.

Are Herbal Weight Loss Diet Pills Safe?

Not all herbal weight loss pills are safe and FDA-examined. Even a herbal supplement containing natural substances like Ephedrine, Yohimbe, Bitter Orange Extract, Hoodia, or excessive Caffeine intake can cause harmful side effects.

So, ensure you talk to a pharmacist or nutritionist before you choose an “all-natural” fat-burning supplement that promises you’ll lose fat quickly.


  1. https://ods.od.nih.gov/factsheets/WeightLoss-HealthProfessional/
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3250069/
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3550246/
  4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2801940/
  5. https://www.nccih.nih.gov/health/bitter-orange
  6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3076034/
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About The Author

Dr. Harshi Dhingra, MBBS, MD is a published peer-reviewed author and renowned physician from India with over a decade of experience. With her MBBS from Bharati Vidyapeeth and an MD from Rajiv Gandhi University, she actively ensures the accuracy of online dietary supplement and medical information by reviewing and fact-checking health publications.
Learn more about our editorial policy
Dr. Kristy June Dayanan, BS, MD is an author with a BS degree from University of the Philippines and an MD from University of Perpetual Help System. Her ability to simplify medical science complexities and dietary supplement jargon for the average reader makes her a valued medical fact checker and reviewer.
Learn more about our editorial policy

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