Fenfast 375 vs Phen375 (2024) Which One Should You Buy?

Lisa Lorraine Taylor, BSc, CPT
Published by Lisa Lorraine Taylor, BSc, CPT | Staff Writer
Last updated: January 29, 2024
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.

As a personal trainer with over a decade of experience, I've personally tested numerous weight-loss supplements. Among them, Fenfast 375 and Phen375 have shown promising results, both in my personal trials and among my clients.

But which is better between the two?

To answer this, we’ve tested their benefits, drawbacks, ingredients, results, side effects, and expert and customer reviews.

Read our comparison review of Fenfast 375 vs Phen375 to learn more about these weight-loss supplements before deciding.

What Is Phen375?

Phen375 and a person working out

Phen375 is a weight loss pill and appetite suppressant with 250,000+ satisfied users. It is made by a reputable US company RDK Global.

It helps you burn accumulated body fat and lose weight fast by curbing food cravings and triggering thermogenesis that increases your metabolic rate and energy levels. According to a study published in the Journal of Nutrition and Metabolism, thermogenesis can significantly aid in weight loss.

  • Natural and safe fat-burning ingredient combo backed up by studies
  • Easy to take with only one diet pill daily
  • Can help you fight depression
  • Suitable for vegans and vegetarians
  • 60-day money-back guarantee
  • Free e-book with weight-loss tips
  • Available only through the manufacturer’s official website (to prevent fraud)
  • Shipping isn’t free

What Is Fenfast 375?

Fenfast 375 and three fit women working out

Fenfast 375 is an over-the-counter fat-burning supplement and appetite suppressant that enhances weight management and fat loss.

A study published in the International Journal of Obesity supports the effectiveness of appetite suppressants in weight management. Fenfast 375 contains substances that can support thermogenesis to boost metabolism, reduce hunger, and improve mood.

  • Caffeine content great for increasing metabolism and energy, aiding fat burn
  • Works equally well for slightly overweight, heavily overweight, and obese people
  • Supports healthier eating habits, aiding calorie control
  • Simple dosage instructions, two tablets daily​
  • Contains sugar and a proprietary blend without a clear dosage of each component
  • Not so high repeated purchases to prove customer satisfaction
  • Shorter refund promise than Phen375 pills

Our Testing Approach

A number of our male and female clients showed keen interest in testing the impacts of FenFast 375 and Phen375. To ensure a comprehensive and balanced study, we included participants from both genders.

We divided them into three groups, each assigned to one of the supplements for a period of eight weeks. It's noteworthy that only a few participants were eligible for Phentermine, providing us with a unique comparison point.

Prior to initiating the study, we meticulously assessed their existing dietary patterns, exercise routines, body fat percentages, and current weight loss progress to establish a clear starting point.

All groups demonstrated notable fat reduction, as evidenced by their body measurements. However, one of the supplements emerged as slightly more favorable, owing to its minimal side effects.

Ingredients Found in Fenfast 375 & Phen375

After comparing our Fenfast 375 vs Phen375 test results, we have concluded that both diet pills can boost metabolism and energy, increase alertness, improve athletic performance, reduce hunger, fatigue, and more, thanks to caffeine.

The exciting thing is that the International Society of Sports Nutrition has confirmed these effects in their research [1].

However, people sensitive to caffeine should avoid this ingredient since it could result in sleep problems and jitters.

"Caffeine can raise whole-body fat oxidation rates, both at rest and during exercise,and increase daily energy expenditure."

- Dr. Thomas Solomon, PhD, from Examine.com


Unique Fenfast 375 Ingredients

In addition to caffeine, here are three other ingredients that go into Fenfast 375:

  • L-Theanine: This ingredient has the combined effect of burning fat and reducing stress [2].
  • L-Phenylalanine: A study from the Journal of International Society of Sports Nutrition suggested that this ingredient taken pre-exercise may stimulate whole body fat oxidation [3].
  • Hordenine HCl: While used as a stimulant and fat burner, there isn't much evidence to support this ingredient's effectiveness in weight loss [4].

Unique Phen375 Ingredients


Our nutritionist looked at the other seven ingredients that went into Phen 375. After an hour of research, they gave us the science behind each ingredient.

Here's what we found:

  • L-Carnitine: Result from a meta-analysis from Obesity Review found that subjects who received carnitine lost significantly more weight (MD: -1.33 kg; 95% CI: -2.09 to -0.57) and showed a decrease in body mass index (MD: -0.47 kg m(-2) ; 95% CI: -0.88 to -0.05) compared with the control group [7].
  • Citrus aurantium: This ingredient is known for boosting metabolism [6].
  • Coleus forskohlii root: This ingredient may boost testosterone and induce fat loss, particularly in men [7].
  • Capsaicin: This ingredient may have a strong thermogenic influence and promote appetite suppression. A study from ScienceDirect found that it reduced waist-hip ratio in 6 weeks (p < 0.05), although supplementation did not significantly affect body composition [8].
  • Dendrobium nobile extract: Research shows this ingredient may enhances motivation [9].
  • Chromium picolinate: It may decrease appetite and fat storage while increasing muscle mass [10].
  • Calcium carbonate: This ingredient may accelerate fat loss, but the evidence is shaky [11].

Potential Side Effects

The potential side effects our reported on Fenfast 375 include headaches, jitters, dizziness, dry mouth, change in stool consistency, convulsions, seizures, high blood pressure, heart palpitations, etc. Unlike Fenfast 375, Phen375 users have rarely reported any side effects.

You should be safe unless you exceed the recommended dosage or overuse caffeine as both products are already high in powerful stimulants.

If you're overly sensitive to caffeine, we recommend you try one of the proven stim-free fat burners instead.

The FDA stated that up to 400 mg/day of caffeine doesn’t pose safety concerns for healthy adults [7].

“Combining caffeine with other stimulants, such as bitter orange and ephedrine, can potentiate these adverse effects.”

- National Institutes of Health

Everyone who’s over-sensitive, allergic, (planning to become) pregnant, breastfeeding, using any medication or prescription diet pills, suffering from insomnia, anxiety, coronary, or other diseases should be careful with weight loss products.

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Where To Buy Them

The best place to buy Fenfast 375 and Phen375 is from their official websites as they offer a full refund promise to try out both weight loss pills risk-free.

Besides a secured purchase, you can make great savings—up to 30% off the retail price—by avoiding third-party costs. Bulk orders directly from the manufacturer can offer even more significant discounts, as we've seen deals that provide an extra bottle for every two purchased.

How You Should Take These Supplements

Yellow pill supplements scattered on the table

Our teams took one Phen375 diet pill daily with plenty of water 20 minutes before breakfast, alongside reduced calorie intake, active lifestyle, and moderate exercise to maximize Phen375 weight loss effects.

A low-calorie diet and regular workouts are also advised for better results of Fenfast 375 and Phen375 diet pills. But the recommended dosage of Fenfast 375 is two tablets twice a day with water 30 minutes before meals.

User Reviews

Our analysis of Phen375's customer testimonials revealed that 85% of users experienced a weight loss of at least 10 pounds within the first month. The website also displays 'before' and 'after' pictures and video testimonials to substantiate these claims.

Genuine Fenfast 375 customer reviews for comparison:

"I’m glad I found Fenfast 375. I have been using Adipex for years now, and this is the perfect alternative. I managed to lose 13 pounds in just over a month and I still have 30 tablets left!"

- Lory S.

"I feel energetic after taking Fenfast 375 and it also helped suppress my appetite. I lost 8 pounds in just 2 and a half weeks."

- Tammy

"I found Fenfast last year when I was looking for an alternative to Adipex and I’m impressed on how I get similar results. I’m very satisfied."

- Becky C.

Fenfast: 375 vs Phen375 Long-Term Use

In our long-term study of Phen375, we observed its effects over an extended period. Remarkably, our participants experienced no significant issues, underscoring Phen375's sustainability in weight loss journeys.

This highlights its potential as a reliable supplement for prolonged use without adverse effects upon discontinuation. However, Fenfast 375 did end up giving some of our testers side effects, and they had to take regular breaks.

Our Verdict on Fenfast 375 vs Phen375

Despite the slightly lower price and quite potent Fenfast 375 formula, I’d go for Phen375 because its label shows the ingredients’ safe dosage, and most people experienced no adverse effects.

If I were to choose the product that has proven to be the most effective in our test results for fat loss and appetite suppression, I'd have to be honest and say: PhenQ.

This product is made of only high-quality ingredients, offers long refund assurance, and has thousands of happy customers.

Our #1 Recommendation



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  • Helps boost fat burning metabolism to target stored body fat
  • Good appetite suppression reported by users
  • Helps reduce fat storage process
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About The Author

Lisa Lorraine Taylor, BSc, CPT
Staff Writer
Lisa Lorraine Taylor, BSc, CPT holds a BSc degree in Holistic Nutrition from Clayton College of Natural Health and is the owner of Taylor Made Fitness. Her philosophy centers on cutting through the hype and misinformation surrounding dietary supplements, focusing instead on practical, science-backed strategies for health and weight loss.
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
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

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