4.7 out of 5
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Phentaslim is a metabolism boosting ‘fat burner’ that has been available for many years. It has a positive track record, customer feedback is generally positive, and it is backed by a 60-day money-back guarantee. Though primarily aimed at those looking to lose hefty amounts of weight, we feel this is a superb supplement for cutting. Read the full review below to find out more. There’s very little not to like about this energy-boosting, fat burning supplement.

  • Effectiveness
  • Safety
  • Price / Guarantee


  • Clinically-proven fat burning ingredients
  • Discounts make it very cost-effective
  • Customer feedback very positive
  • 60-day money-back guarantee
  • Free worldwide shipping


  • Only available direct from the manufacturer
  • Not suitable if you’re sensitive to caffeine
2 comments Page updated Aug 11, 2020.
First published Mar 16, 2019.
So you’ve done the hard work bulking up, and now you’ve reached the cutting stage. You want to get that lean, ripped look, and the way to do that is to lose weight. But you want to lose weight without losing muscle mass. Many people will choose to use a supplement to help them reach this goal.

Phentaslim is marketed at those wishing to lose a substantial amount of weight, the couch potato rather than the athlete. So you might be thinking this one is just for those with an excessive love of doughnuts. Think again. I’ve given it a go, and it’s a great choice for cutting as well.

Phentaslim Overview

Made by Optimum Nutra, Phentaslim has been available for several years and is classed as a fat burner.

Phentaslim uses a metabolic diet formula. Without getting scientific and boring, the ingredients work to boost your metabolism. They increase the rate at which your body burns the excess energy you’ve stored as fat.

About the Manufacturer

Optimum Nutra Inc has been around for almost a decade. Although this may seem a relatively young company, ten years in supplements is a long time. It’s not unknown for supplement companies to spring up from nowhere, launch a product, and disappear within six months without a trace.

The ingredients and quantities used in Phentaslim are clearly outlined on the packaging. This is important since other companies hide ingredient profiles in a ‘proprietary formula’. If you’re like me you’ll prefer to know what you’re putting into your body, and Phentaslim provides these details.

The product is made in GMP facilities in the USA that have been FDA inspected. You can trust you’re buying a quality supplement that adheres to all the safety regulations. Outside of the US, Phentaslim is manufactured and distributed worldwide from the UK. Both the US and International products are the same. Same bottle, same company, same formulation.

Optimum Nutra do not auto-ship their products, so you’ll only receive what you pay for. The supplement industry has a problem with companies that trick customers and sign them up to a subscription, or offer ‘free-trial’ prices that are misleading. Optimum Nutra Inc. do not partake in these sort of activities, which is a major plus point. We haven’t found any reports of customers feeling scammed.

Phentaslim Key Features

So, what does Phentaslim claim it can do?

  • Breaks down carbohydrates and fatty acids
  • Supercharges fat burning – Burns more calories and targets fat, making getting shredded easier
  • Boosts Energy – Prefect for that pick me up, whether heading to the gym or trying to get through the work day

An earlier big hit from this company is Superfruit Slim. It’s still available to buy. I mention it, because, Superfruit Slim is suitable for vegetarians and vegans. Phentaslim is not. I can’t figure out why the company wouldn’t use vegan friendly caps with a later product. It doesn’t bother me – I’m a caveman when it comes to meat. It’s just, why limit a product to fewer people when it’s easy not to have to.

How to Take Phentaslim

A daily serving is three capsules. Take one before breakfast, one before lunch, and the third capsule either before dinner or about an hour before exercise. Because of the caffeine content, consumers should avoid taking this product in the evening. Customers may also want to start with a lower dosage to assess personal tolerance levels.

Phentaslim Benefits:

  • Well-balanced use of quality ingredients
  • Effective fat burner that boosts energy
  • Money-back guarantee and free worldwide shipping

My Phentaslim journey

Let’s cut to the chase. I’m in my late-forties now and although not out of shape, I am developing a bit of middle-aged paunch. My wife isn’t bothered, she says it makes me even more cuddly, but I’ve always been athletic. I’m not one for sitting around; I keep busy, I eat fairly well. It’s just not as simple as it used to be to maintain a slim waistline.

We’ve reviewed Phentaslim before and found it to be effective. Optimum Nutra recently rebranded this supplement and sent us a three bottle package to review. Although a welcome freebie, this has not influenced our opinion: if something’s rubbish, we’ll tell you it is, no bull.

The Phentaslim arrived securely packaged in a sturdy plain box. There was no branding on the outside of the box, just a shipping label that doesn’t reveal what’s inside. If you don’t want people knowing what you’ve ordered, this company has your back.

The look of the product is okay. You can see the red capsules through the clear bottle. You get 90 capsules in every bottle. The label is just that: a label – it’s red, it’s black, and offers no added value. On the label you’ll find the ingredients, directions for usage, the company’s main address, and the best before date. It’s not unlike many other supplements I’ve seen. What matters most is what’s inside the capsules.

So, Phentaslim in one hand, middle-aged paunch in the other, I decided to follow the instructions and began my course. I’ll let you know how I got on throughout the rest of this review.

Phentaslim Ingredients: Full Disclosure

Phentaslim contains a well-balanced blend of high quality ingredients. Looking down the list of what has been used, it’s clear the people who’ve formulated this supplement know what they’re doing.

Each daily serving of three capsules contains a total of 1800 mg of the Phentaslim formula. The individual ingredient quantities provided below are for the combined three capsules daily serving.

  • Green Tea (375 mg): Green tea is high in a group of antioxidants called catechins. Studies have suggested that catechins increase thermogenesis in the body, whilst caffeine increases energy expenditure by boosting the metabolism for a few hours.
  • Caffeine (270 mg): Numerous studies have shown that caffeine boosts energy levels and alertness, as well as mildly boosting the metabolism.
  • L-Theanine (225 mg): This amino acid may play a small role in weight loss, as well as increasing feelings of relaxation. It may also reduce the negative side effects of caffeine, although there is seemingly no strong clinical evidence to support this claim.
  • L-Carnitine (200 mg): There is some evidence that supplementation of acetyl-l-carnitine can reduce body fat, although the strongest results were seen in the elderly. The ingredient also boosts energy levels and is used to treat fatigue.
  • L-Tyrosine (200 mg): Some people use Tyrosine as an appetite suppressant, but there is little clinical evidence that it is effective for this use. Large doses of tyrosine may be useful for increasing alertness, especially in people who are sleep deprived.
  • Panax Ginseng (120 mg): 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.
  • Guarana Seed (100 mg): A berry that is naturally high in caffeine, it is often an ingredient in energy drinks and diet pills.
  • Magnesium (80 mg)
  • Cayenne Pepper (50 mg): Capsaicin, which is found in Cayenne pepper, is thought by some to play a role in weight loss. Some studies suggest it could suppress the appetite mildly, whilst others suggest that the heat causes a thermogenic reaction in the body, burning more calories for a period of time.
  • Niacin (20 mg): Vitamin B3, or Niacin, is responsible for helping to produce energy from consumed food, as well as helping keep the nervous and digestive systems healthy. Niacin can be sourced in adequate amounts from a balanced diet.
  • Zinc (15 mg)
  • Black Pepper Extract (6 mg): Black pepper extract (piperine) is used for increasing the bioavailability of nutritional compounds. In other words, it increases the amounts of nutrients that are absorbed into the body in the digestive tract. It may also increase the absorption of various drugs, which may lead to potential side effects.
  • 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 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, so you should be able to get your daily guideline amounts from a healthy balanced diet.
  • Thiamin (Vitamin B1) (1.3 mg): Thiamine is important for helping to break down and release energy from food. This may be relevant for maintaining a healthy metabolic rate.
  • Vitamin B12 (10 mcg): Vitamin B12 is naturally present in many foods, primarily meat, fish and dairy products. It has several roles, including aiding in releasing energy from consumed food, and keeping the nervous system healthy. A deficiency could hinder weight loss.

What Are The Side Effects Of Phentaslim?

Each capsule contains around 90mg of caffeine – perfect to kick-start your day or gym routine, but if you’re sensitive to caffeine then this may not be the right supplement for you.

You might want to cut back on the coffee if you’re an avid drinker of the dark stuff. Caffeine tolerance is a personal thing; just listen to what your body is telling you. If you take Phentaslim and drink coffee, you might feel too alert and jittery, and find the experience unpleasant. Then again, you could feel like a tornado, blast through a workout or jog an extra fifteen minutes, and really feel the benefit.

I took Phentaslim as directed: One capsule before breakfast, one at lunch, and a third early evening. I felt fine, maybe a little too caffeinated at one stage (though I blame the extra coffee I had in the afternoon), but otherwise fine. I definitely had more energy at the end of my workday than I would normally have.

It’s advised to start with 1-2 capsules per day if you’re new to using supplements.

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 anyone who is sensitive to caffeine and other stimulants. Consumers should avoid other stimulants and all other sources of caffeine whilst taking this product to minimise the chances of side effects. Not suitable for those under the age of 18.

Phentaslim: does it work?

The ingredient profile of this supplement can indeed produce positive results. When used as advised (with exercise and a balanced diet), Phentaslim can assist you in the gym to get that cut look you’re seeking. The fat-metabolising and energy-boosting properties work in tandem to push you further to burn the fat.

My Results

My experience is it does work, and if you put the effort in you could get some incredible results. In total, I took Phentaslim for just under three weeks before writing this review. I used to be a competitive athlete a few decades ago, so I’m by no means lazy (old habits never die). But I wasn’t hitting the gym during my three-week course. My greatest exertion of energy and effort came perhaps on the Saturday midway through the three weeks, when I dismantled an old wooden shed, using just a claw hammer and my hands. The rest of my time was spent sat at my desk, walking around the office, or at home chasing squirrels off from the bird feeders.

So what happened? I’ve lost weight. I consider there to be two types of weight loss: daily, and actual. Everybody’s weight goes up and down throughout the day with, you know, eating and stuff. Actual weight loss, to me, is weight that is lost and stays lost. Overall, I’ve lost 3lbs of actual weight. This may sound small, but bear in mind I wasn’t really trying. so I’m rather happy with my results. Pleased, in fact. It shows this supplement works as stated.

Now, I can imagine if I had put in the effort, added in some lifting sessions, some proper cardio; I genuinely think I’d be looking at some significant weight loss. Of course, in those circumstances, It’d be difficult to say whether it’s the supplement or the exercise that’s responsible for the weight loss. But my lacklustre, guinea pig trial has clearly demonstrated that Phentaslim can work of it’s own accord. Throw in some serious exercise and effort, the potential is incredible.

Customer Feedback

Never mind me, other customers agree that this supplement gives you the extra help to shift some weight or boost your work-out. Testimonials easily found on the web say:

It’s the best thing I have done as I have lots more energy and it has stopped me snacking. Weight loss has been gradual and I’ve lost a total of 8lbs!

I have lost half a stone in weight – WITHOUT dieting, but by just taking two capsules each morning.

Found the weight dropping off me and not buzzed like other pills I have tried… dropping two dress sizes has helped a lot!

Have been using Phentaslim to shift some excess body fat from bulking stage. So far, it’s looking good. Maintaining strength my abs are looking more defined. They boost my energy levels as well, I can push myself further.

Phentaslim 60-Day Money-Back Guarantee?

Optimum Nutra offers a 60-day money-back guarantee on this supplement, which starts from the order date. The guarantee is valid for one opened bottle, and any additional bottles returned need to be unopened. This is ample time to give it a try to see how it works for you.

All you need to do is contact customer support for a returns authorization number to get the process started.

Where to Buy Phentaslim?

Phentaslim can be bought through the official website. It is available on its own or as a package. The discounted packages and free shipping make this a very cost-effective supplement.

  • One bottle, enough for one month, costs $59/£39
  • Three Bottles (2+1 bottle free) cost $99/£77
  • Five bottles (3+2 bottles free) cost $149/£117
  • Our Verdict On Phentaslim

    I’m impressed with Phentaslim and the manufacturer, Optimum Nutra.

    Phentaslim is the real deal. Every ingredient in this formula has been chosen for its fat burning and appetite suppressant qualities, and are backed by clinical studies.

    If you’re looking for a thermogenic pill to help burn more calories, Phentaslim is a superb choice. Getting lean and ripped isn’t easy but using this fat burner can shred those pounds so you look and feel great!

    Optimum Nutra look after their customers. They respond to questions promptly, do not operate any auto-ship or subscription nonsense, and the returns policy is simple and fair.

    There’s no question, this supplement will give you awesome energy and targets your body fat. The pricing is acceptable given the quality of this product, and the discounted packages make it very cost effective. It’s worth buying in bulk anyway, these supplements work best when used for a couple of months rather than just the one (your body needs time to get to grips with any changes you make).

    In all, I have no problem in recommending Phentaslim.

    Product Website

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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.

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2 comments on 'Phentaslim'

  1. But is Phentaslim JUST an appetite suppressant and a laxative? I do not want to lose weight that way, buy if it really does speed up your metabolism, then yes I am very interested

  2. can you use this if you are diabetic and have thyroid problem also taking antidepressant tablets? My husband has all of the above and struggling to lose weight can you suggest any safe way for him? Many thanks

    Mrs Britt Long