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5 Side Effects of Diet Pills You Can Experience

Isaac Robertson
Published by Isaac Robertson | Co-Founder & Chief Editor
Last updated: August 2, 2023
We personally test every product featured in our reviews and guides. By ordering products anonymously and getting a group of independent testers, we are able to get first-hand experience and provide data-driven recommendations. Learn more.

A restricted diet complemented by exercise and particular fat burners may indeed help you lose weight faster and fight obesity.

But that’s not the whole truth.

Remember that some common ingredient combinations found in fat-burning supplements can trigger hazardous side effects.

That’s the price no one would like to pay for quick weight loss, right?

To help our readers avoid health risks, we’ve reviewed relevant literature and asked experts to share their expertise and knowledge on scientifically proven adverse reactions you can expect when you consume certain compounds supposed to shed extra pounds (plus tips on avoiding them).

Read on.

Quick Summary

  • The side effects of weight loss pills include vomiting, nausea, dizziness, dry mouth, headache, dehydration, insomnia, increased heart rate, and diarrhea.
  • To get rid of some side effects of weight loss pills, stay hydrated, avoid caffeine, and mind your dosage intake.
  • Weight loss pills boost energy and metabolism levels, which in return helps burn fat and calories.

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

When considering fat burner supplements for losing weight, it's important to note that individual experiences may vary.

While some users may achieve positive results in their weight loss journey, others may not experience the same effects.

A fat burner isn't a magic solution, but rather a tool to support your efforts when combined with a balanced diet and regular exercise.

Here’s a detailed list of the most common side effects research has proven and several ingredients found in fat burners linked to each side effect.

1. Dehydration and Headache

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

Besides Phentermine, Ephedrine, and other prohibited drugs, a combination of some stimulative plant-based compounds like Caffeine, Yohimbine, Bitter Orange, etc., regularly used in high doses to help you burn fat, can cause dehydration that results in headaches and migraines [1] [2].

The diuretic effect of such an appetite suppressant combined with inadequate water intake and grueling exercise, especially during hot weather, may also lead to other frustrating physical and mental health issues, including:

  • 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 [3] [4].

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 [5] [6].

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

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

Researchers have found that some common thermogenic ingredients in fat burners intended to boost your fat metabolism and curb hunger cravings are linked to high blood pressure (BP), irregular heartbeat, stroke, and other cardiovascular issues, especially in unhealthy obese people [7] [8].

Studies have shown that stimulant-based compounds like Caffeine, Green Tea extract, Yohimbe, Ephedrine, Fenfluramine, Phenylpropanolamine (PPA), and others can raise your blood pressure and heart rate [9] [10].

“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 [11] [12].

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

4. Psychological Side Effects

woman covering her face while crying

Some potent chemicals in fat burners (e.g., Ephedrine, Citrus Aurantium, Yohimbine, Yerba Maté, Kola Nut, Caffeine, and others) stimulate your central nervous system to trigger thermogenesis, increase fat oxidation and energy expenditure, and inhibit fat absorption from the food you eat to promote weight loss.

Furthermore, these compounds help you increase the feeling of fullness and curb hunger by targeting serotonin and norepinephrine neurotransmitters in your brain, plus raising the stress hormone cortisol.

Science claims that such overstimulation may bring behavior changes like irritability, anxiety, mood swings, panic attacks, aggressiveness, restlessness, agitation, other mental imbalances and emotional disturbances, even suicidal thoughts (giving individuals an idea of causing self-harm).

5. Liver Damage

man holding his right waist in pain

There’s scientific evidence that the prolonged use of particular fat burners containing usnic acid, Green Tea, and Guggul tree extracts can lead to severe hepatotoxicity that may result in acute liver failure requiring emergent transplantation, even death [13].

Typical symptoms included fatigue, nausea, vomiting, jaundice, and abdominal pain.

An additive commonly used in fat burners - Chromium polynicotinate - may cause acute liver injury. Kombucha tea is also hepatotoxic as it contains usnic acid.

Aegeline is another substance extracted from leaves of an Indian plant Marmelos Correa connected to liver inflammation and the other similar negative effects mentioned above.

Various other fat burner compounds may lead to liver damage, interacting with heavy metal contaminants, Garcinia Cambogia, and other plant extracts [14].

Battle-tested fat burners:

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

Experts claim that a clean, calorie-restricted diet paired with regular exercise is the safest and most effective way of burning fat and maintaining a healthy weight long-term.

In short, follow a healthy lifestyle instead of seeking shortcuts to fat loss.

However, if you’re struggling to reduce excess body weight without consuming fat burners, make sure you do all you can to prevent their possible side effects.

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

It’s also better to opt for a substitute stimulant-free supplement with a lower dosage and avoid products that contain any banned or harmful ingredients that can interact with your prescription medications and adversely affect your health and well-being.

Also, pregnant and breastfeeding women, patients with diabetes, cardiovascular issues, anorexia, or any similar chronic disease diagnosis should stop taking weight loss supplements or other over-the-counter dietary supplements.

Moreover, it’s highly recommended even for healthy people to consult a healthcare professional before taking such supplements.


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.

Weight Loss Pills Side Effects Summary

Besides boosting metabolism and energy, burning calories and fat, and shaping up your figure, fat burners may also compromise your health and safety if you ignore the quality and purity of the substances listed on the label.

So, steer clear from supplements of questionable content and effectiveness that may cause a variety of mild to severe adverse reactions.

To stay on the safe side, focus on a balanced diet and exercise plan, and always consult your doctor or pharmacist before heading to the store to find out what’s the best product choice for you and what preventative measures to take.

Share your opinion, experiences, and questions about fat burners with us.


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