Updated: 01/18/2018

The Phentaslim list of claimed benefits reaches as far as Neptune, so our team set out to determine whether these promises were legit – or just space debris. We dug into the ingredients and side effects right away. We tried to search for honest and unbiased customer reviews, but you can only buy this product directly from the manufacturer. Not letting that get us down, we examined the scientific studies and read through the research. We couldn’t find a single study carried out on this fat burner, but nevertheless, here is what we found.

Phentaslim – Benefits of a Thermogenic Fat Burner Readers: Click here to find out why we're giving away samples of our product, Burn HD.

What is Phentaslim?

To start, Phentaslim is a metabolism booster that promises everything under the sun – but does it work?

We’ll start with the ingredients:

Other ingredients found in Phentaslim include cayenne pepper, panax ginseng root, l-tyrosine, l-theanine and l-carnitine. The ingredients do have some research behind them – which we’ll get to in a little bit.

Supposedly it helps by boosting energy levels, decreasing hunger and reducing excess body fat, but without scientific studies on the formula, it’s impossible to know if this is true.

Optimum Nutra, a leading supplement manufacturer, is the company behind Phentaslim. The official website sells the supplement, but also offers special deals and discounts on multiple-bottle purchases. The only downside is that you can’t really find it anywhere else, making it hard to find real customer reviews.

Phentaslim – Benefits of a Thermogenic Fat Burner Competitors

Superfruit Slimread
Burn HD (Sample offer)read

Phentaslim Ingredients – “The Proof is in the Formula”

The first thing tackled was the effectiveness of Phentaslim ingredients. “It’s promising to see a formula containing a blend of stimulants, vitamins, and minerals,” said our Research Editor. “Even better is the research showing it works.”

One customer stated, “This for me is a really good product that does not give me that crazy over-amped feeling of my heart beating rapidly or shortness of breath.”

“Found the weight dropping off me and felt absolutely amazing at the same time – dropping 2 dress sizes blew me away,” commented another.

There are additional reviews of Phentaslim offering praise.

“Losing 32 pounds has dramatically changed my life,” commented a customer.

Phentaslim – Benefits of a Thermogenic Fat Burner Customer Testimonials

Phentaslim Reviews – “Dieters Approve”

Dieters tell us the inside story of the effectiveness of a supplement. They also inform others of their results. We took a closer look at Phentaslim reviews to get both sides of the story. One person stated, “6 KG Lost Without Dieting! I have lost more than one stone/ 6 kilos in weight -WITHOUT dieting, but by just taking two capsules each morning.”

“I am trying to lose that stubborn last 10 pounds, I think I may try this product,” commented a customer.

“1 1/2 Stone Lighter And Keeping It Off! First week on it and I’m rather impressed,” reported a dieter.

Another said, “I feel good, no jitters, great energy levels and very impressed.”

Research shows a connection between favorable reviews and long-term success. There are positives if dieters see positive changes after using Phentaslim.

The Science – “Clinically-Proven”

The company states Phentaslim ingredients are clinically-proven, so we’ll take a closer look. The blend contains 15 natural extracts, vitamins and minerals. The first two being green tea and caffeine. Both are well known, researched, and shown to help naturally accelerate metabolism, increase energy and curb appetite. L-Theanine, L-Carnintine, and L-Tyrosine are amino acids, but function differently. L-Theanine promotes attention and cognitive function, while L-Carnitine supports recovery, protects lean muscle and boost metabolism.

Panax Ginseng and Guarana are extracts promoting mental performance and increases in energy. Magnesium supports nervous system functionality and cayenne pepper helps suppress appetite. The added B-Vitamins help promote overall health, as well as boost energy levels.

Also: read our Burn HD Weight-Loss Kit review »Phentaslim – Benefits of a Thermogenic Fat Burner Ingredients

The Bottom Line – Does Phentaslim Work?

Clinically-proven ingredients, supportive comments and an affordable price tag? Is Phentaslim the real deal? There’s a chance that this one will help you lose weight and reach your goals. The only concern we noticed were a few comments mentioning about the effectiveness of the supplement, but users didn’t add if they followed directions; ate healthy or exercised.

If you want to lose those extra pounds, there’s another one out there catching our eye. It contains clinically-tested ingredients, backed by positive reviews.

Among the best products we’ve seen this year is one called Burn HD. It contains four ingredients. All clinically-tested with results commonly found in journals such as Obesity and the Journal of Medicine. It’s shown to help accelerate metabolism, curb appetite, and ignite fat loss. Dieters tell us they see great results.

Also, the company behind Burn HD offer customers a 2-Week Sample, which is a good sign.

Learn More About Burn HD »
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Phentaslim – Benefits of a Thermogenic Fat Burner

What are the side effects of Phentaslim?

Phentaslim side effects, based on user reviews, were mild.

What are the ingredients in Phentaslim?

Phentaslim ingredients are green tea [1], caffeine, l-theanine, l-carnitine, l-tyrosine, panax ginseng, guarana seed, magnesium, cayenne pepper, niacin, zinc, black pepper extract, vitamin B6, riboflavin, thiamin, and vitamin B12.

How do I know if Phentaslim – Benefits of a Thermogenic Fat Burner is right for me?

Choosing the right product is the #1 question asked by DietSpotlight readers. We recommend trying any product before buying it and know that finding a product with a sample offer is near impossible - so we created our own product, Burn HD, with scientifically backed ingredients.

Click here to get your sample of our powerful fat burner today.

Does Phentaslim work?

The Phentaslim formula is not bad. It contains green tea and caffeine, two important ingredients. [2] However, you can find these in hundreds (if not thousands) of other products.

How much does Phentaslim cost?

Phent costs $59.99 for 90 capsules.

How should I take Phentaslim?

You should take Phentaslim three times a day, once 20 minutes before breakfast and lunch and once in the late afternoon. It is not suggested to take Phentaslim after 5pm.

Can I take Phentaslim if I have a health condition?

You should ask your physician if you are under the age of 18, if you are taking prescription medications, have other underlying health problems, are pregnant, or nursing.

Does Phentaslim come with a guarantee?

Phentaslim has a 60-day money back guarantee.

Phentaslim – Benefits of a Thermogenic Fat Burner Ingredients

Phentaslim is a "revolutionary diet pill" containing natural ingredients. There are clinical studies on the official website connecting the formula to weight-loss.

Phentaslim – Benefits of a Thermogenic Fat Burner Ingredients and Supplement Facts

Serving Size: 1 Capsule
Serving Per Container: 90
Amount per Serving% DV
Green Tea375mg*
Panax Ginseng120mg*
Guarana Seed100mg*
Cayenne Pepper50mg*
Black Pepper Extract6mg*
Vitamin B61.8mg*
Vitamin B21.7mg*
Vitamin B11.3mg*
Vitamin B1210mcg*

Other Ingredients: Gelatin and magnesium stearate

We really researched the Phentaslim ingredients in order to provide the important details and specifics.

Green Tea Extract

Sometimes referred to as camellia sinensis, green tea is an unfermented variety that has been consumed in China and India for centuries. It is typically steeped in hot water and consumed for its health benefits.

What is it Supposed to Do?

There are quite a few different health benefits that pertain to green tea. For instance, this herb provides both caffeine (a stimulant) and catechins (antioxidants). These components have been shown to help boost metabolism and promote weight-loss. Furthermore, the antioxidants in this plant offer other benefits as well. They may assist with lowering bad cholesterol, improving immune system health, controlling blood sugar levels, and even preventing cancer. [1]

Clinical Research

According to the University of Maryland Medical Center, “Clinical studies suggest that green tea extract may boost metabolism and help burn fat. One study found that the combination of green tea and caffeine improved weight loss and maintenance in people who were overweight and moderately obese.”


Also known as 1,3,7-trimethylxanthine, caffeine is naturally found in plants such as coffee seeds, tea leaves, guarana, yerba mate and cocoa beans. It is a stimulant and mild diuretic. Many people get this ingredient daily from energy drinks, coffee and tea beverages, as well as sodas.

What is it Supposed to Do?

Often caffeine is added to weight-loss supplements to help suppress appetite, boost energy levels, enhance focus and stimulate metabolism. Since this ingredient is a stimulant, it affects the central nervous system. Some research has shown that it can aid with weight reduction by increasing thermogenesis. [2]

Clinical Research

PubMed.gov reveals that, “High caffeine consumers reduced weight, fat mass, and waist circumference more than low caffeine consumers; resting energy expenditure was reduced less and respiratory quotient was reduced more during weight loss. High caffeine intake was associated with weight loss through thermogenesis and fat oxidation and with suppressed leptin in women.”

Panax Ginseng

To start with, panax ginseng is a natural herb that grows in regions like Korea and northeastern China. It is also called Asian ginseng. This ingredient is found in countless diet supplements and energy drinks. It contains active components such as panaxosides and ginsenosides.

What is it Supposed to Do?

There are quite a few health claims regarding panax ginseng. For instance, this herb is supposed to help treat depression, combat chronic fatigue, improve memory, boost libido and treat erectile dysfunction.

Clinical Research

“People who take ginseng often say they feel more alert. Several studies report that Asian ginseng may slightly improve thinking or learning. Early research shows that Asian ginseng may improve performance on such things as mental arithmetic, concentration, memory, and other measures,” reported the University of Maryland Medical Center.

Guarana Seed

Also called Brazilian cocoa or paullinia cupana, guarana is a plant that grows in regions such as Brazil. This ingredient is found in various diet pills and energy drinks. It provides a significant amount of caffeine, which is a stimulant.

What is it Supposed to Do?

Typically guarana is added to dietary supplements for weight-loss to help boost metabolism, improve energy levels and enhance focus. It may also assist with appetite reduction.

Clinical Research

“Because caffeine is a stimulant that has been shown to improve mood and aid weight loss, guarana may very well also have these effects. As a weight loss supplement, caffeine may work best when combined with the polyphenol compounds in green tea. Combining guarana with polyphenols may have a similar effect,” says WebMD.

Amino Acids

Phentaslim contains three amino acids, which include l-theanine, l-carnitine and l-tyrosine. These are the building blocks of protein, which means they aid the body and muscles with repairs and maintenance.

What is it Supposed to Do?

Amino acids are included in this supplement to help with relaxation, improved cognition, fuel metabolism, muscle recovery, appetite suppression and increased energy levels. Some research shows that amino acids help fight arthritis, boost the immune system, lower cholesterol, reduce aging effects, improve muscle strength and support weight-loss.

Clinical Research

Researcher Robert Coker, PhD from the University of Arkansas for Medical Sciences says that, “Essential amino acids, included as part of a meal replacement, along with whey protein, improved the synthesis of muscle and led to a greater loss of fat.”

Phentaslim – Benefits of a Thermogenic Fat Burner Scientific Abstracts

Green Tea

There are some reports of the effects of EGCG (epigallocatechin-3-gallate) at a submicromolar level. However, most tests require concentrations of >10 or 20 micromol/L to test and demonstrate this effect. In humans, tea polyphenols go through sulfation, methylation, glucuronidation, and ring fission. EGCG’s peak plasma concentration is around one micromol/L. Thus, the potential significance of each of the proposed mechanisms for the prevention of cancer in humans is examined in light of up-to-date bioavailability data for tea polyphenols and the possible limits of animal models of carcinogenesis. New research efforts are sought out to discuss the misunderstandings of cancer prevention. [1]


Studies had shown that L-theanine had significantly inhibited blood pressure increase in a group of participants. Caffeine had a tendency for similar, yet smaller, effects of the blood pressure triggered by mental tasks. After the tasks, it was displayed that L-theanine had reduced tension-anxiety scores compared with placebo groups. It was concluded that L-theanine didn’t just decrease anxiety, but attenuates increased blood pressure in high-stress response adults. [2]


Magnesium has been reported to improve serum lipid profiles when intake is increased, offering an important role in cardiovascular diseases. Dietary magnesium has been suggested to help the prevention of stroke and is crucial for skeletal growth and development. It may also be important in the development of obesity, diabetes mellitus, and metabolic syndrome. There is additional data that suggest changes in lifestyle can benefit blood pressure control, help weight-loss, and improve chronic disease risk. [3]

Guarana Seed

Amiodarone’s plasma and tissue concentrations, as well as its major metabolite (mono-N-desethylamiodarone), were observed, measured and analyzed. A very noticeable decrease in the peak plasma concentration (73.2%) and the term of systemic exposure (57.8%) to amiodarone was discovered in rodents who were treated with amiodarone and Paullinia cup and. There had been an observance of tissue reduction as well. It was determined that the interaction of amiodarone and Paullinia cup and extract showed a significant decrease in amiodarone bioavailability in rats. [4]


Currently, niacin is available in three formulations – extended release, long acting, and immediate release. They possess a vast difference in their safety and efficacy profiles. Immediate release niacin is typically used three times daily and is accompanied by negative flushing, elevations in blood glucose levels, and gastrointestinal symptoms. The long-acting variety can be ingested just once per day, typically associated with substantially decreased flushing; however, its metabolism raises the risk of hepatotoxic effects. The last variety of niacin, which is also administered once daily, possesses an absorption rate intermediate between the others. Also, it’s associated with less flushing and gastrointestinal symptoms minus the increase of hepatotoxic risk. [5]

Summer Banks Dietspotlight Author
About the Author:

Summer Banks, Director of Content at Dietspotlight, has researched over 5000 weight-loss programs, pills, shakes and diet plans. Previously, she managed 15 supplement brands, worked with doctors specializing in weight loss and completed coursework in nutrition at Stanford University. full bio.

11 Phentaslim – Benefits of a Thermogenic Fat Burner Reviews

  •  Unhappy (Verified User)

    I have used one bottle and haven’t dropped a pound! The product is a waste of time. I have been eating healthy and exercising 3 times a week. Don’t waste your money. It does however replace a cup of coffee in the morning! Good caffeine boost but that’s about it

  • Fast results?

    How long before I would expect to see results?

    • Alana

      I’ve been taking them for almost a week now. I’ve had loads of energy and am able to go for brisk, half hour walks.yes I can feel my clothes getting looser. I have been drinking lots of water and peppermint tea and eating healthy, small portions throughout the day. Feel fine so far. It’s like anything. Can work for some people, maybe not others. I’ve also read many good reviews on other sites.

    • Maribel (Editor)

      Hello. All users are different and can experience different weight-loss results. If you feel like you’ve reached a plateau, you might want to try other products if this one doesn’t work out for you. Another product that helps with burning fat is Dietspotlight Burn.

    • Marie

      I have been taking 3 months and only lost 5 pounds
      Don’t bother waste of money

  •  Fantastic :)

    well i ordered my 1 month supply and i had received these tuesday just gone… i have taken one in the morning and one round my lunch time. i dont take the 3rd one as i wanted to adjust slowly to them..since being on these tablets i feel my body already reacting positivly to these . not only less appetite now but im going to the toilet more lol..sorry to go a bit gross but since going toilet more i notice old poo aswell leaving my body and my stomach doesnt feel as bloated aswell and actually looks flatter.. i do suffer with IBS badly and these do help with spasams for some reason (maybe with some of the herbal ingrediants)..im drinking 2 literz a day or even more now when before i would only drink a cup at night. i also feel more energy… i am a 38 year old woman and 2 kids.. full time job and housewife aswell… these tablets are defo doing something positive FOR ME… fantastic 🙂

  •  Happy happy!

    i really like it im so happy im losing weight finally happy happy

  • Karen Redrup

    I have been eating healthy and exercising frequently and I haven’t lost a thing – complete waste of money.

    • Victoria (Editor)

      Hi Karen, we’re sorry that you had no results with this product. All users are different, and sometimes, don’t achieve the weight loss results they were hoping for. If you’re looking around for other alternative fat burners or metabolism boosters, you might want to check out Dietspotlight Burn.

  •  Waste of money
    Marie (Verified User)

    Don’t bother buying phentaslim. Iv been taking this product for 3 months taking 1 tablet 20 mins before breakfast 1 tablet 20 mins before lunch and 1 tablet 20 mins before evening meal with a full glass of water before each tablet and kept to a strict diet and excersize but only lost 5 pounds in 3 months.
    I’m not convinced it was the tablets that made me lose the 5 pounds but the strict diet and excersize that did.
    Expensive product and a waste of time

  • My experience
    Curvy redhead (Verified User)

    I used this product after doing a lot of research and checking reviews. I needed something that would suppress my sugar cravings that had little or no side effect. I only take 2 a day so a bottle has lasted me 45 days ( although some days I’ve not taken it). I am doing Weight Watchers but cravings got so bad and I was spending £1-3 a day on chocolate, the weight was piling back on. Phentaslim was the last resort and for me it has worked, I knew it wasn’t a diet suppliment or meal replacement. I purely needed help with irrational cravings and thankfully it worked for me. I had no side effects other than having no sugar cravings and feeling fuller meant I didn’t snack between meals and most of time started wanting to have healthier meals.