Updated Nov 10, 2020.
Published Nov 15, 2012.
Dr. Krystal Crawford, ND, MS
Medically reviewed by Dr. Krystal Crawford, ND, MS, written by Rachel Butler.

Phentaslim is a powerful metabolism booster. This means it will work to raise your metabolic rate. All sounds like too much science? Probably. Put simply, a faster metabolism is the perfect way to lose weight, and to lose it properly.

We’ll get straight to the point: for ‘fat burning’, we’re yet to find a better product.

We’ve loved Phentaslim ever since it was first made available many years back. It’s now better than ever, having been revised to make it vegan-friendly. All considered, there’s very little not to like about this weight loss supplement.


  • Over 130,000 customers
  • High-quality, natural ingredients
  • Expertly-crafted, precision formula
  • Safely made in a GMP certified facility
  • Company does not auto-ship – you only receive what you order (no hidden subscription)
  • Free shipping and 60-day money-back guarantee


  • Sold direct from the manufacturer – no price competition
  • Not for those sensitive to caffeine
Phentaslim is a metabolism-boosting diet pill that is available exclusively online from the official product website. The website describes numerous benefits of using the product and has been used by many thousands of customers to maximize their potential weight loss.

The company who make Phentaslim is about as blunt as they come when it comes to weight loss: there are no miracle cures, you can’t just take a pill and expect great results. Great results come with a bit of extra effort.

This is why they market Phentaslim at people who are actually serious about weight loss and not those who just want to swallow a pill and then eat a wedge of cake. This product requires discipline, from you, for it to work effectively.

Below we take an in-depth look at Phentaslim to see how effective it is at helping with your weight loss goals.

Phentaslim Key Features

Phentaslim is manufactured by a company called Optimum Nutra Inc. The Phentaslim website starts off with a testimonial from a happy customer who claims to have lost 18 pounds over a period of five weeks and extolls the virtues of using Phentaslim to achieve this.

It is said that this can be achieved as the product increases the metabolism, reduces excess body fat, decreases hunger cravings, and increases energy levels. The product also claims to support good mental balance, good concentration, and co-ordination.

Phentaslim Key Points

  • Manufactured by Optimum Nutra Inc.
  • 90 pills per bottle
  • Contains a range of clinically proven ingredients

The product is manufactured in Government inspected facilities that have met the highest standards of production. The company can be contacted using the information provided on the official website, and some customers will like that there is a direct sales line to take phone orders.

Phentaslim Benefits

  • Uses clinically proven ingredients in the right amounts
  • Marketed as an effective fat burner and appetite suppressant that boosts energy
  • Full 60-day money-back guarantee and free worldwide shipping options

Optimum Nutra Inc. has an excellent reputation for customer service, and we were unable to find any customer complaints about the company. We sent an inquiry via the contact form regarding some of the ingredients and received a detailed reply back within a couple of hours. It feels like they are aiming for a personal touch and put the customer first.

How to Take Phentaslim

Take three capsules per day. The manufacturers do not state on the website how best to distribute these three capsules, but we suggest taking two with breakfast, and the third capsule either with lunch or about an hour before exercise. Customers may also want to start with a lower dosage to assess personal tolerance levels.

What does Phentaslim claim to do?

The manufacturer of Phentaslim describes the following benefits for the product:

  • Boost metabolism – Ramp up your metabolism so that you burn more calories and increase your fat loss.
  • Longer lasting energy – Boosts energy levels without that crash and burn feeling, so you’re ready for anything!
  • Suppress appetite – Suppresses your appetite so that you stop snacking between meals.
  • Support mental performance – Supports good mental balance, good concentration and co-ordination.

Does Phentaslim work?

Both the ingredients list and the customer reviews we have located suggest that Phentaslim aids in weight loss without the side effects seen in other supplements.

Appetite suppression seems to be very effective for many consumers too, meaning this could help you to stick to a lower calorie diet plan that you may be following.

Phentaslim Ingredients

Each daily serving of Phentaslim is comprised of three capsules. You are advised to split them over the course of the day, ideally before meals and taken with a glass of water.

The actual makeup of the supplement is said to be a “metabolic diet formula” and the blend of ingredients certainly agrees with this:

Thermogenic Complex

  • Green Tea 15:1 Extract (375 mg) and Caffeine Anhydrous (270 mg): These two powerhouses have been combined in a synergistic dosage that produces significant effects on weight maintenance through thermogenesis, fat oxidation, and sparing lean body mass.
  • Guarana Extract (400 mg): A berry that naturally contains caffeine, has a longer-lasting action, and is uplifting for both body and mind.
  • Korean Panax Ginseng (1,200 mg): Korean Panax Ginseng is associated with improved cognition in fatigued subjects and slight decreases in muscle damage after exercise. It also appears to reduce fatigue, and consumers report feeling calmer after consumption.
  • Cayenne Pepper Powder (50 mg): Capsaicin, which is the active compound in Cayenne pepper, has been shown to have an active effect on weight loss. Some studies show it could suppress the appetite, whilst others show that the heat causes a thermogenic reaction in the body, burning more calories for a period of time.
  • Black Pepper Extract (24 mg): Black pepper extract (piperine) is used for increasing the bioavailability of nutritional compounds. It increases the amounts of nutrients that are absorbed by the body in the digestive tract, and is added here to aid the correct absorption of the rest of the ingredients.
  • Gingko Leaf Extract (120mg): Increases blood flow and circulation throughout the body. Has cognitive benefits and is high in anti-oxidants.

Although each of the above ingredients have all been clinically proven to be effective, the significance is in the way they are blended in the optimal combination. This also allows for the correct ingestion and processing as a whole, leading to the overall theremogenic effect.

Amino Acid Complex

  • L-Theanine (225 mg): One of the body’s natural building blocks, L-Theanine has a relaxing effect and works in combination with the caffeine-based ingredients to offset the “jittery” effect that caffeine alone might have.
  • N-Acetyl L-Carnitine (200 mg): Another amino acid, L-Carnitine is involved with the mitochondrial oxidation of long-chain fatty acids. It also reduces fatigue to aid with physical activity.
  • L-Tyrosine (200 mg): Naturally produces catecholamines in the body, such as dopamine and adrenaline, and is a precursor to thyroid hormones – all of which are proven aids to weight-loss.

Amino acids are critical to the correct metabolisation of fats, as well as effective brain functioning. This allows the body to produce enough fat-burning hormones. It’s like getting a hormone kick-start in a natural manner and in harmony with the body’s needs.

Vitamin and Mineral complex

  • Thiamine – Vitamin B1 (1.3 mg): The NHS states that thiamine is important for helping to break down and release energy from food. This may be relevant for maintaining a healthy metabolic rate, as well as helping with the catabolism of fats.
  • Riboflavin – Vitamin B2(1.7 mg): This vitamin is used for keeping the eyes, skin and nervous system healthy, as well as helping the body to release energy from carbohydrates. It is naturally present in milk, eggs, rice, and fortified breakfast cereals.
  • Niacin – Vitamin B3 (20 mg): Niacin is responsible for helping to produce energy from consumed food, as well as helping keep the nervous and digestive systems healthy.
  • Vitamin B6 (1.8 mg): Vitamin B6 has several important functions in the body, including allowing the body to use and store energy from protein and carbohydrates in food. Whilst taking excess amounts of vitamin B6 will not infinitely improve this ability, a deficiency could make it more difficult to lose weight.
  • Vitamin B12 (10 mcg): Vitamin B12 is naturally present in many foods, primarily meat, fish and dairy products. It has several roles, including aiding the release of energy from consumed food, and keeping the nervous system healthy.
  • Zinc (15 mg)
  • Magnesium (80 mg)

This vitamin and mineral complex has been blended to work in conjunction with the thermogenics. Put simply, the body needs adequate amounts of these (the B vitamins in particular) in order to provide energy.

What we think of the ingredients

The “triple action” effect of the thermogenic, amino acid and vitamin/mineral complexes contained in Phentaslim produce a very impressive combination.

Normally we see ingredients skimped on, with the more expensive ingredients – usually the ones that actually work – reduced in volume. This is not the case here. It’s rare that we see a product that packs as much punch as Phentaslim.

So What Does All This Mean?

Whilst many diet pill manufacturers offer statements and make dramatic claims about how their product works to aid weight loss, very few offer evidence for their claims. The manufacturers of Phentaslim have included numerous links to the clinical trials they have referenced.

Caffeine will increase the body’s metabolism for a period of a few hours after consumption. The content for each capsule is about the same as a cup of coffee, so spacing out the doses, taking two with breakfast and one with lunch or before exercise will maximize the energy and metabolism boost throughout the day. Theanine will help to counteract some of the “jitters” a few people experience. The inclusion of black pepper extract will likely increase the absorption of caffeine, enhancing its effects.

Green tea and cayenne pepper will both increase thermogenesis in the body, burning more calories in the process. Cayenne pepper may also have a small appetite suppressing effect, although studies suggest that this is small.

Acetyl-L-Carnitine and Tyrosine are both amino acids, so can be used by the body to create muscle mass when the consumer is undertaking muscle building exercises.

The vitamins provided in this supplement are of an appropriate level compared to the recommended daily intake. Consumers should ideally not combine this product with other sources of caffeine or other B vitamin supplements.

Phentaslim Side Effects

Whilst some of the ingredients used in Phentaslim can cause side effects in a very few consumers who are very sensitive to caffeine, the dosages are well-balanced to be effective whilst making side effects uncommon.

As with anyone who is taking prescription medication, you should consult your doctor before taking a product of this type. Theanine claims to help counteract some of the potential side effects of caffeine, including any jitters.

Caution: Always swallow the capsules with water. Do not take if pregnant or nursing. If you have any medical conditions or are taking any medication, consult your doctor before use. Not suitable for anyone suffering from any heart-related health issues, including, but not limited to, high blood pressure. Not suitable for those under the age of 18.

Phentaslim Customer Feedback

Numerous customers have left their feedback for Phentaslim here at Diet Pills Watchdog. A selection of these comments are below:

Started taking 1 of these each morning on Wed this week and am down 2 pounds already! Has given me the ability to get out of recliner and be the wife and grandmother Ive always wanted to be! Spotlessly clean house and flowerbeds are weeded. Been to the gym every day since starting these! Has really helped with my hunger and curbed appetite. I pray they continue to help like this!

I received my order in the mail super fast which was awesome. Best of luck to everyone who takes these, they’re great!

So after a full two month course on these pills, I am very happy to announce that I have lost two and a half stone in two months! I would recommend these to anyone hoping to get a head start on their weight loss as the extended energy, fuller feeling of stomach and ease of use make these HIGHLY commendable.

I ordered this product mid-April and am really liking it so far! Have lost noticeable weight (that people comment on). I do exercise regularly anyway so haven’t changed anything there, it’s just given me a much needed boost. The only thing I will say is that – as a big caffeine drinker myself – do not drink coffee while taking this product, at first I couldn’t sleep/was feeling a bit jittery. However when I cut the coffee down that all stopped! Good product if taken correctly!

Two weeks ago I was 20st 11.4lbs. Weighing this morning I am 19 st 11.6lbs. 0.2 pounds away from losing a stone in two weeks.
I have drank only water and eaten clean over the two weeks. The pills are amazing for helping to suppress your appetite but I recommend you have a small amount to eat after the 20 min recommendation of taking them or you will experience a weird stomach until some food is digested. The energy I am experiencing from these pills has really helped me down the gym and has finally kicked me into gear for losing weight. I highly recommend these pills for helping towards your overall diet and exercise plan but that’s all it is. A booster for your diet and exercise. You put in the effort and these pills will help you get the most out of what you do. 9.9/10.

Phentaslim Money-Back Guarantee

The manufacturers offer a 60-day money-back guarantee on this supplement, which starts from the order date. This is valid for one opened bottle, and any additional bottles returned should be unopened.

Customers should obtain an RMA number from the company’s customer service department before sending the package, and should mark the RMA number clearly on the outside of the package.

Where To Buy Phentaslim

Customers can order Phentaslim from the official Phentaslim website, and have a choice of several multi-buy purchase options that can make massive savings.


We’ve been informed that there are time-limited savings available. We would advise readers wanting to purchase Phentaslim to check the website for real-time pricing.

Current Offers

  • A one bottle starter pack costs £39/45€/$59.
  • The two bottle package for £77/87€/$99 now includes an extra bottle free, so three bottles in total
  • A five bottle package now costs £117/137€/$149, you’re paying for three and geting two more included free
  • FREE DELIVERY on all orders, anywhere in the world.

In general, Phentaslim is a very cost-effective product.

Customers can securely pay using Visa, Mastercard or American Express credit and debit cards card. There is no auto-ship program or automatic repeat ordering, which we particularly like.

Watchdog Verdict

Overall, we are very impressed with both Phentaslim and its manufacturer, Optimum Nutra Inc. The company clearly associate themselves with their own products on their official website, provide a company address, and follow high manufacturing standards for diet pills. They offer a 60-day money-back guarantee, the returns policy is clear and easy to follow, and all the information is available on the website. The claims the manufacturers make about the product are supported by references to clinical trials and are not outrageous or ridiculous.

As for Phentaslim itself, it appears to have a solid ingredients profile, using appropriate dosages of the active ingredients. Numerous ingredients used in the product have strong clinical support, such as caffeine and green tea. The ingredients used also have a strong safety record.

The product has been around for quite a while, and the number of positive reviews from happy customers that we found are very encouraging. The customer reviews also support the idea that if used properly and alongside a healthy diet and regular exercise, Phentaslim can help to accelerate the consumer’s rate of weight loss.

We have no hesitation in making Phentaslim the number one choice for consumers, and the editors top selection.

Phentaslim Frequently Asked Questions (FAQ)

Does Phentaslim really work?

Yes, when combined with a healthy diet and exercise. This isn’t a magic diet pill and like any effective diet pills requires work from the consumer too. The list ingredients work to boost metabolism along with suppressing appetite to help increase calorie burning and reduce calorie intake.

How do I take Phentaslim tablets?

It’s recommended to take one capsule with a glass of water (8 ounces) before breakfast and another one capsule with water before lunch. The capsule size is similar to other such supplements and so shouldn’t pose any problems taking them.

We do suggest following the manufacturers advice and drinking plenty of water when taking Phentaslim, this will ensure you’re hydrated.

How quickly will Phentaslim work for me?

There are no claims of losing huge amounts of lbs in just 2 weeks from the manufacturer. We like this, as everyone is different making such claims can be misleading. That said their testimonials show consumers losing 12lbs in 3 weeks and others 28lbs in 9 weeks.

Do I have to change my diet when taking Phentaslim?

The manufacturer recommends eating a healthy diet combined with regular exercise to get the best results. This supplement can help with reducing food cravings, so making changes to your diet will be easier to tackle. There are massive long-term benefits to eating a healthy well balanced too.

Are the ingredients in Phentaslim safe?

All the ingredients are 100% safe and unless you’re particularly sensitive to caffeine (see below) unlikely to suffer any side effects.

How much caffeine is in Phentaslim?

There is caffeine in Phentaslim and so may not be suitable for those sensitive to this ingredient. Actual caffeine comes from a few ingredients, these are:

Phentaslim’s caffeine content:

Caffeine Anhydrous (270mg)
Guarana Extract (22mg)
Green Tea Extract (16mg)
Total approximately: 308mg per daily serving of 3 capsules, so just over 100mg per capsule. This is the equivalent of a strong, filter coffee.

It is recommended adults consume no more than 400mg of caffeine a day, though this really depends on your individual tolerance.

Since caffeine is a great ingredient for weight loss, we would suggest cutting down elsewhere, swapping regular coffee for decaf, black tea for decaf, green, or a fruit infusion. We feel the caffeine in Phentaslim is more beneficial than getting it from a cup of coffee, especially if you’re one for adding cream and sugar, and maybe a donut on the side – something you should really stop doing, to be honest.

How long can I take Phentaslim for?

The manufacturer doesn’t indicate a limit on how long you can take Phentaslim. We generally advise not taking supplements for longer than 6 months without taking a break. This does very much depend upon your health and the amount of weight you’re looking to lose.

Can I buy Phentaslim from South Africa?

According to the manufacturer issues with local delivery in South Africa has meant they have needed to remove this shipping destination for the time being. They are looking at alternatives and so hopefully shipping to South Africa will resume soon.

Are there any Phentaslim discount codes?

We have asked the manufacturer for a discount code and they are looking into this, so watch this space!

Official Website

Disclaimer: Our reviews and investigations are based on extensive research from the information publicly available to us and consumers at the time of first publishing the post. Information is based on our personal opinion and whilst we endeavour to ensure information is up-to-date, manufacturers do from time to time change their products and future research may disagree with our findings. If you feel any of the information is inaccurate, please contact us and we will review the information provided.

Have Your Say

575 comments on 'Phentaslim'

  1. I’m extremely sensitive to caffeine and these pills did nothing for me. I felt no energy and i still felt hungry.

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