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.

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

Phentaslim Pros

  • Over 100,000 customers
  • Clinically proven weight loss quantities
  • Made in a “GMP” certified facility with solid ingredient profile
  • 60-day money-back guarantee

Phentaslim Cons

  • Only available direct from the manufacturer – no price competition
  • Contains caffeine
Watchdog Approved Diet Pills

Jump to section…

Phentaslim Review

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 32 pounds over a period of 5 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 Facts

  • 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.

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.

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

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.

So What Is Phentaslim and What Are The Ingredients For Phentaslim?

The ingredients used in Phentaslim are listed below. Each daily serving of three capsules contains a total of 1800 mg of the Phentaslim formula. The individual ingredient quantities provided below are per three-capsule 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 slightly 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. The effects shown in studies are small, and some studies are inconclusive.
  • 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. However, there are also studies that show cayenne has little or no effect upon weight loss attempts.
  • 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 easily sourced in adequate amounts from a balanced diet. Persistent excessive consumption of niacin has been linked with increased rates of obesity in American Children.
  • 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 people should be able to get their daily guideline amounts from a healthy balanced diet.
  • Thiamin (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, but in the majority of cases people can obtain all the thiamine they require from their daily diet.
  • 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. It may be that a deficiency hinders weight loss, but taking excess amounts could be, according to the NHS, potentially harmful.

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.

phentaslim holding bottleCaffeine 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.

Does Phentaslim Have Any 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.


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.

Any Phentaslim Reviews From Customers?

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.

So 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.

Where Can I 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

  • Two bottles (buy one get one free) costs £39/45€/$59.
  • The two bottle package for £77/87€/$99 now includes an extra bottle free
  • A five bottle package now costs £117/137€/$149.
  • 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.

What About A 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.

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.

Watchdog Approved Diet Pills

Click here to Visit Phentaslim Official website!



Phentaslim is distributed by a company called Optimum Nutra Inc. and manufactured in Government inspected facilities that have met the highest standards of production. 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. The product has been around for quite a while, and the number of positive reviews from happy customers that we found are very encouraging.

  • Effectiveness
  • Safety
  • Price / Guarantee

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.

601 comments on “Phentaslim”

  1. Victoria says:

    I take 75g of levothyroxine daily plus one low dosage anti depressant- Citalopram. Is it safe to take Phentaslim?

  2. Jules says:

    so far I have lost 2kgs in 4 weeks. Because I cannot exercise like I used to at the gym 5 days a week and can only do Yoga now, I was really hoping this would work. So far it is! 😀 I still keep to a very healthy vegan diet so this may also help.
    I hope this helps answer some questions as I was very wary myself to start with.

  3. hilde stevens says:

    graag info

  4. Christina says:

    Hi I’ve read the reviews about that pill but I can’t find a review of what happens when you stop that.I mean do you take all your weight back?

  5. Lee Meek says:

    Can I take Phentaslim on blood pressure medication?

  6. Wendy says:

    Can a Diabetic use your product???will it help lower blood sugars Thaks

  7. Aarti says:

    Can phentaslim pills be taken if you are following or starting a ketogenic diet?

  8. Sarah says:

    Hi I have read all the comments and am going to buy this but can’t see a reply about when people stop t what happens? Do people put on what they have lost? do they put on weight quickly?

  9. Gail Dazeley says:

    Can I take phentaslim while taking fluoxetine ?

  10. Tracey Jones says:

    Can I take Phentaslim on blood pressure medication

  11. Kezia C. says:

    Posting to see if the comments are genuine! Adding to this to say my first bottle arrived yesterday.. Starting them in the morning… Hoping to lose 14lbs…

  12. Ely says:

    Wich one recommend that is best for suppressant appetite between Phentaslim and ultra omega burn ?
    Thank you

  13. DILWYN says:

    What is the price.

  14. DILWYN says:


  15. Sue says:

    I take 75 ml of Levothyroxine a day, is it safe to take Phentaslim slimming tablets.

  16. Calli says:

    Does this product work with the Keto diet?

  17. Angel Vargas says:

    For a company that prides itself in customer service they lack business vision. Tried to place an order and for administrative reasons they do not ship to Puerto Rico. They don’t know we are part of the USA and that all mayor carriers come here daily. I’m waiting to see if this change. Will let you know.

  18. Patricia says:

    Are these addictive?

  19. adri gordon says:

    I get severe heartburn soon after taking this product. Any reason for this? Please advice and thank you

  20. Michelle says:

    I have TBI, low-active Thyroid, PTSD, joint pain, chronic spine pain. Due to massive amounts of stress, I’m putting on weight. -20 lbs to be exact. Will this product help? I will ask my neurologist, but wanted your “in-depth” thoughts”.

  21. Hi I am currently on a low dose of blood pressure tablets amlodopine 5mg and ramipril 1.25mg od. my blood pressure is currently in normal range since i started the low dose of medication. i haven’t got a liver disease but the hospital is monitoring my blood result as it fluctuates (most test are normal, MRI and liver protein result good result. i really need to loose some weight as i am 168cms hight and about 94kg.



    1. Emily Claire says:

      hi, I was just looking at the comments and saw yours. Looking at the ingredients of Phentaslim I think you should ask your doctor before taking it as it’s quite high in caffeine and you don’t want it to effect what you are taking now.

  22. Maria C olon says:

    Why it’s so expensive? Same price for 1 bottle 2 or 3 bottles? Why?

  23. Kathy Heinrich says:

    I have IBS. Can I take this with convenience.

  24. Margaret Mellor says:

    I am on a very low dosage of tablets for my blood pressure and have taken XLS Medical but didn’t find it worked. I need to loose a stone in weight. I am 71 and comfort eat since loosing my husband 4 years ago. I don’t look my age and take care of myself . I just won’t to loose that stone and I would be very happy. Do you think these tablets will help me. I did get the go ahead to take XLS medical. Regards Margaret

    1. Hollie Richardson says:

      Hi Margaret, I comfort eat too and I did end up trying Phentaslim and lost 5 kilos! But because you are on blood pressure tablets I would recommend to ask your doctor first as it contains really high amounts of caffeine. I tried XLS Medical too but didn’t do anything for me. Hope this helps 🙂

      1. Margaret says:

        Thank you . I did ask my Doctor about XLS Medical and he there was nothing in it to harm me. I will check with him and will all look at both tablets to see what’s in them

  25. tonianne beyer says:

    Do they sll this at the GNC store?

  26. tonianne beyer says:

    Can u buy this at the GNC store or elswhere?

  27. Britt long says:

    Can this be used when you have thyroid problem and diabetes ?

  28. Kathryn Davies says:

    It does tell you on the site and on the pot how to take the pills, 1 20 minutes before breakfast with water, same lunch time and evening before 5pm!

  29. Clare says:

    Roughly how long does the product take to arrive, I have a wedding end of march and would to lose some weight before then.

  30. Linda says:

    Sorry 32mg daily

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Be nice. Keep it clean. Stay on topic. Please do not spam.