Phentaslim Review 2023: Does This Supplement Really Burn Fat?

Reviewed by Kathy Shattler, MS, RDN

A team of qualified and experienced fact-checkers carefully reviews our content before it is published on our website. At MIDSS, we rely on the latest and most reliable sources, which are cited in the text and listed at the end of each article. We also do not accept plagiarised and misleading content from our authors and contributors. Read more about our fact check and editorial process.

We include products that we believe will be of use to our readers. If you make a purchase after clicking on one of the links on this page, we may receive a small commission. This is our advertising disclaimer.

Editor Rating:
Rating Methodology

About this rating

We want to offer you the most suitable health products. That’s why we have developed a rating methodology in MIDSS to evaluate the products. You can see it here.

  • = Quality
  • = Support Research
  • = Reputation
  • = Price

  • Natural ingredients
  • Vegan-friendly
  • Potent metabolism booster
  • Expends stored body fat for energy
  • Clinically approved ingredients
  • 60-day money-back guarantee
  • Owned by Optimum Nutra
  • Started in 2011
  • Facilitates weight loss
  • Promotes energy levels
  • Suppresses appetite
  • Boosts metabolism

About The Brand

Phentaslim is a weight loss supplement owned by Optimum Nutra. This product was launched in 2011, and since then, people have been using it for fat and weight loss. This brand is among the many diet pills used in the UK and elsewhere.

The brand defines this product as an effective weight loss supplement because of its organic ingredient list. It contains green tea, caffeine, l-theanine, acetyl l-carnitine, l-tyrosine, Panax ginseng, magnesium, guarana seed, cayenne pepper, and black pepper.

This weight loss supplement attributes this vast list of ingredients for its weight loss effects. However, to see the extent of the weight loss will depend on you as the user. You will get better results if you live a healthy lifestyle with exercise and a healthy diet. But if you expect the same when you are not living a healthy life, you may be unable to burn the extra calories you take in or get rid of the fat storage.

The supplement is vegan-friendly, and you only take one diet pill 20 minutes before all the main meals. The brand does not offer any purchase subscriptions. Phentaslim’s distributors ship it worldwide with a 60-day money-back guarantee.

What Is Phentaslim?

Phentaslim is a weight loss supplement that promises to do the following

  • Help you lose weight
  • Help accelerate your metabolic rate
  • Target the stored body fat and expend it as energy
  • Help mitigate weight gain

The fat-burning supplement is vegan. You may purchase single tubs or get them in bundles at a discount from the company’s site. Anyone can place their orders with free shipping and get a 60-day money-back guarantee.

How Does Phentaslim Work?

Phentaslim prides itself on offering the above using its all-natural, clinically proven ingredients for fat loss. This dietary supplement blend provides the body with a supplementary supply of minerals and vitamins with immeasurable weight loss properties.

They all work in tandem to boost your energy production as it turns the body’s energy source from the carbohydrates you ingest to the stored fat in your fat cells. But you cannot get there if you are not on a healthy lifestyle of eating a healthy diet and exercising. It would help if you created a calorie deficit in your diet by reducing the number of carbohydrates(carbs) you ingest while increasing your lean proteins, healthy fats, vitamins, antioxidants, and mineral intake.

The calorie deficit helps the body seek an alternative energy source which becomes your stored fat cells.

The manufacturer suggests you take one or two capsules daily for the best results.

Is Phentaslim Safe?

Phentaslim’s creators and users in some Phentaslim reviews attest that it is undoubtedly a safe fat burner.

On the flip side, the company offers a disclaimer on the usage of the product. One instance to take caution is if you have any serious medical condition. In such a case, they suggest consulting a healthcare provider with knowledge of the use of dietary supplements and their implications.

Also, note that Phentaslim, like all other dietary supplements, is not Food and Drug Administration (FDA)-approved or regulated. So much so that you need to ensure that quality standards exist and that the supplement is preferably third-party lab tested for contaminants. Also, ensure that you acquire your fat burner from a valid and verified source. Most importantly, use it in the prescribed quantity at the suggested times to boost energy levels.

You should also note any service marks on the product. These labels, such as a trademark, promote the legitimacy of a supplement.

Lastly, if you have a body mass index (BMI) of less than 18.5, are pregnant or lactating or are under the age of 18, you should not take this supplement as per the manufacturer. If you have a medical condition or are taking medications, it is advised that you consult with a healthcare provider before taking this supplement.


  • Aids in weight loss
  • Boosts energy levels
  • May help you avoid weight gain
  • Vegan and vegetarian-friendly
  • Jam-packed with potent antioxidants, vitamins, and minerals
  • 60-day money-back guarantee
  • Free worldwide shipping


  • It does not have enough appetite-suppressing ingredients
  • The caffeine content may be high for some individuals

Phentaslim Product & Coupon


Best Reputation


  • Natural ingredients
  • Vegan-friendly
  • Potent metabolism booster
  • Expends stored body fat for energy
  • Clinically approved ingredients
  • 60-day money-back guarantee

Phentaslim Ingredients

This proclaimed effective weight loss supplement contains 17 main ingredients in its formula. All the ingredients are natural and vegan-friendly. They collectively offer the body a faster metabolic rate, fewer hunger pangs, and more energy production from expended excess calories and stored body fat. 

You may also notice an improvement in your mental performance, exercise recovery, less lean muscle loss, and overall well-being.

When you want to ascertain that the brand’s claims are true, you should start by taking a deeper look at the ingredient list. And not just the ingredients’ names but read about the scientific findings on each ingredient.

Phentaslim ingredients

Please note that you might find information that supports and conflicts with the claims. So, to get the most accurate conclusion, please consider both sides and check the report’s date. Here is a brief list including the 17 main natural ingredients and their benefits to the human body.

Korean Panax Ginseng

The Korean Panax in this fat burner is great at supporting your mental performance and overall well-being. Ginseng is potent at boosting energy levels[1], lowering blood sugar[2], regulating cholesterol levels[3], reducing stress[4], and promoting relaxation.

It also boosts immunity and alertness.

Guarana Seed Extract

The guarana seed extract is an exceptional fruit extract that is naturally abundant in caffeine, providing extra energy while also improving memory[5], alertness, and mood. It also acts as an appetite suppressant and prevents insulin resistance[6].

Green Tea Extract

Catechins are a specific type of antioxidant in green tea. Norepinephrine[7], a hormone that aids in fat burning[8], is increased by these catechins in your body. Your body will burn fat more effectively as norepinephrine levels rise.

Catechins stimulate fat oxidation, boost thermogenesis without raising heart rate, and lower body fat, cholesterol levels, and blood pressure[9].

Caffeine Anhydrous

Anhydrous caffeine increases energy and metabolism while suppressing appetite. There is 270 mg of caffeine in this supplement, about as much as is in two eight-ounce cups of coffee. Caffeine helps people lose weight since it is a metabolic stimulant[10] that raises exercise endurance, and improves exercise performance while increasing vigilance, focus, and alertness. 

It also has an impact on appetite by decreasing your sense of hunger. Additionally, those who regularly exercise may be able to train harder and for longer.


This ingredient promotes improved cognition[11] and attention, increases metabolism[12], and decreases appetite.

When combined with caffeine, this non-essential amino acid has excellent calming and attention-promoting properties. This ingredient can lessen the possibility of anxiety and reduce the perception of stress.

Other Ingredients

Here are the rest of the ingredients in Phentaslim:

  • L-Carnitine is a  natural amino acid used in this formula that promotes energy production[13] and mental performance[14] while speeding up your metabolism. However, its effects on weight loss[15], body mass index (BMI), and body mass, especially in obese adults, are modest.
  • L-tyrosine, in this formula, is excellent for the brain. It may help reduce a foggy brain and improve attention[16].
  • Magnesium regulates blood sugar[17] and insulin levels in the body. The effect of regulation between these entities is reduced fat storage from the food you consume.
  • Cayenne pepper extract is thermogenic, increasing the body’s core temperature. The effects of thermogenesis are that it forces the body to start to cool down, which causes the body to use up more calories leading to the body torching stored fat[18]. It is also a potent appetite suppressant.
  • Black pepper extract is a supplementary ingredient used in weight loss supplements as it increases the bioavailability of all other ingredients. They get absorbed faster and thoroughly, ensuring the effects are felt more thoroughly and for a longer time.
  • Ginkgo leaf extract is a potent antioxidant that may help reduce anxiety and improve heart health[19], circulation, and inflammation[20]. Obesity is a disease of inflammation[21].
  • B vitamins: (niacin, B6, B2, B1, B12) Niacin helps with lowering cholesterol levels[22], and B6 helps with the conversion of food into energy[23], and it also helps burn excess body fat. B6 may also help with muscle growth as it increases the absorption of amino acids[24] and proteins. Vitamin B1 and B2 help the body release energy from food, and vitamin B12 helps with mood[25], concentration, energy, and the immune system.
  • Zinc helps with boosting and sustain the body’s energy levels[26]. It enables the body to process proteins, fats, and carbohydrates into energy to pump up its levels.

Alternatives To Phentaslim

NamePhenQPhenGoldInstant Knockout
ProsFast shipping
60-day money-back guarantee
Helps with weight loss, appetite, and cognition
Natural ingredients
Free shipping
Strong fat burner
Offers fast, great fat-burning results
Controls hunger
Caffeine is in high doses for mental focus
ConsIt has a proprietary blend
It is expensive
Appetite-suppressant ingredients would have made the formula betterThe caffeine content may be too high
Full reviewPhenQ Review PhenGold Review Instant Knockout Review

Check Price

Check Price

Check Price

Health Benefits Of Phentaslim

The health benefits that Phenstaslim’s manufacturer promises you are:

  • A faster metabolism
  • Improved cognition health
  • Appetite suppression
  • Boosted energy levels
  • Supports lean muscle growth and promotes workout recovery
  • Improved fat oxidation

Remember that to get all these benefits, you must be on a healthy diet and be active.


You should take 3 capsules of this supplement daily, according to Phentaslim makers. Although the exact timing of taking these hasn’t been specified, we anticipate that it should be done throughout the earlier part of the day, given the high caffeine dosage.

It is best to have a continuous and spaced delivery of caffeine as it provides your body with a steady stream of nutrients to keep you in a fat-burning mode, but if taken late in the day it may keep you up at night.

Phentaslim Reviews: What Do Real Users Say?

Numerous Phentaslim reviews are available online, and there is a mix of good and bad comments. These comments are typically left behind on a feedback form, emails, or direct input on review sites.

Insomnia reloaded. I don’t care anymore whether Phentaslim works or not. I just want to my normal life of sleeping at night and not having to deal with drowsiness during the daytime when I’m supposed to be active and productive in my workplace. I purchased Phentaslim from its official website because I wanted this supplement to help me lose some weight. I can’t sleep even after taking some sleeping pills. I consulted my doctor, who advised me that Phentaslim contains caffeine, and that’s the ingredient responsible for my recent insomnia. I’m no longer taking the capsules. Even if I want to lose weight, but not at the expense of not getting a good night’s sleep.

Carolyn P

Without a doubt, I am confident that Phentaslim is an effective weight loss supplement, but I’m very concerned about the potency of ingredients that uses this. I experienced scary palpitations while I was using it. I did notice increased energy levels as well as a higher body temperature and increased sweating, good indicators that I was burning more calories. The palpitations caused me to also develop severe anxiety, and I was unable to complete a proper cycle of the supplement. I may try back in the future since it is good but scary at the same time.

Gabrielle P.

I’ve lost over 40pounds since I started using phentaslim. I sometimes only need 1 with a mouthful of water. Lost my belly fat in no time.

Nev Richards

Final Thought

To celebrate the best weight loss goals using this and any dietary supplement, you need to eat healthily and stay active. Phentaslim promises a boost in energy, fat and weight loss, improved mental acuity, and general well-being. Their ingredients are clinically proven, so the supplement is potent enough to target fat burning and effectively torch stored fat.

This weight loss supplement is a great product, but it still has its fair share of negative feedback, which we think is insufficient to warrant Phentaslim as a scam. The feedback on insomnia and jitters are isolated scenarios personal to the users. It may or may not affect you. Plus, everyone’s experience with any supplement is unique as is their sensitivity to caffeine.

Still, it would be best to get professional medical advice before using this product. Also, if it helps, search for any service marks mentioned for brand credibility.

Frequently Asked Questions

How long does it take for Phentaslim to work?

The effects of taking Phentaslim are felt a few hours after you start using it. However, the weight loss effects will only be seen after a few weeks if you are eating healthy and staying active.

What is Phentaslim good for?

Phentaslim is good for fat and weight loss, boosting energy levels, and improving mental health.

How to take Phentaslim?

You swallow one capsule three times a day before your main meals.

Can Phentaslim have negative effects?

Yes, just like other dietary supplements, it does have side effects like nausea, dizziness, upset stomach, and diarrhea.

Where can I buy Phentaslim?

The best place to buy Phentaslim is the official website. You can also purchase it from a reputable seller that is verified.

+ 26 sources

MIDSS adheres to strict procurement guidelines and relies on peer-reviewed studies, academic research institutes, and medical associations. We work mainly with peer-reviewed studies to ensure the accuracy of the information. We avoid the use of tertiary references. You can read about how we ensure the accuracy and timeliness of our content in our editorial process.

  1. Bach, H.V., Kim, J., Myung, S.-K. and Cho, Y.A. (2016). Efficacy of Ginseng Supplements on Fatigue and Physical Performance: a Meta-analysis. Journal of Korean Medical Science, [online] 31(12), p.1879. doi:10.3346/jkms.2016.31.12.1879.
  2. Bang, H., Kwak, J.H., Ahn, H.Y., Shin, D.Y. and Lee, J.H. (2014). Korean Red Ginseng Improves Glucose Control in Subjects with Impaired Fasting Glucose, Impaired Glucose Tolerance, or Newly Diagnosed Type 2 Diabetes Mellitus. Journal of Medicinal Food, [online] 17(1), pp.128–134. doi:10.1089/jmf.2013.2889.
  3. Kwon, Y.-J., Jang, S.-N., Liu, K.-H. and Jung, D.-H. (2020). Effect of Korean Red Ginseng on Cholesterol Metabolites in Postmenopausal Women with Hypercholesterolemia: A Pilot Randomized Controlled Trial. Nutrients, [online] 12(11), p.3423. doi:10.3390/nu12113423.
  4. Baek, J.H., Heo, J.-Y., Fava, M., Mischoulon, D., Choi, K.W., Na, E.J., Cho, H. and Jeon, H.J. (2019). Effect of Korean Red Ginseng in individuals exposed to high stress levels: a 6-week, double-blind, randomized, placebo-controlled trial. Journal of Ginseng Research, [online] 43(3), pp.402–407. doi:10.1016/j.jgr.2018.03.001.
  5. Boasquívis, P.F., Silva, G.M.M., Paiva, F.A., Cavalcanti, R.M., Nunez, C.V. and de Paula Oliveira, R. (2018). Guarana (Paullinia cupana) Extract Protects Caenorhabditis elegans Models for Alzheimer Disease and Huntington Disease through Activation of Antioxidant and Protein Degradation Pathways. Oxidative Medicine and Cellular Longevity, [online] 2018, pp.1–16. doi:10.1155/2018/9241308.
  6. Bortolin, R.C., Vargas, A.R., Ramos, V., Gasparotto, J., Chaves, P.R., Schnorr, C.E., Martinello, K., Silveira, A.K., Gomes, H.M., Rabelo, T.K., Grunwald, M.S., Ligabue‐Braun, R., Gelain, D.P. and Moreira, J.C.F. (2019). Guarana supplementation attenuated obesity, insulin resistance, and adipokines dysregulation induced by a standardized human Western diet via brown adipose tissue activation. Phytotherapy Research, [online] 33(5), pp.1394–1403. doi:10.1002/ptr.6330.
  7. Ranjbar-Slamloo, Y. and Fazlali, Z. (2020). Dopamine and Noradrenaline in the Brain; Overlapping or Dissociate Functions? Frontiers in Molecular Neuroscience, [online] 12. doi:10.3389/fnmol.2019.00334.
  8. Ryu, V. and Buettner, C. (2019). Fat cells gobbling up norepinephrine? PLOS Biology, [online] 17(2), p.e3000138. doi:10.1371/journal.pbio.3000138.
  9. Xu, R., Yang, K., Ding, J. and Chen, G. (2020). Effect of green tea supplementation on blood pressure. Medicine, [online] 99(6), p.e19047. doi:10.1097/md.0000000000019047.
  10. Hodgson, A.B., Randell, R.K. and Jeukendrup, A.E. (2013). The Metabolic and Performance Effects of Caffeine Compared to Coffee during Endurance Exercise. PLoS ONE, [online] 8(4), p.e59561. doi:10.1371/journal.pone.0059561.
  11. Baba, Y., Inagaki, S., Nakagawa, S., Kaneko, T., Kobayashi, M. and Takihara, T. (2021). Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study. Journal of Medicinal Food, [online] 24(4), pp.333–341. doi:10.1089/jmf.2020.4803.
  12. Li, M.-Y., Liu, H.-Y., Wu, D.-T., Kenaan, A., Geng, F., Li, H.-B., Gunaratne, A., Li, H. and Gan, R.-Y. (2022). L-Theanine: A Unique Functional Amino Acid in Tea (Camellia sinensis L.) With Multiple Health Benefits and Food Applications. Frontiers in Nutrition, [online] 9. doi:10.3389/fnut.2022.853846.
  13. Jain, S. and Singh, S.N. (2014). Effect of L-carnitine Supplementation on Nutritional Status and Physical Performance Under Calorie Restriction. Indian Journal of Clinical Biochemistry, [online] 30(2), pp.187–193. doi:10.1007/s12291-014-0437-1.
  14. Pennisi, M., Lanza, G., Cantone, M., D’Amico, E., Fisicaro, F., Puglisi, V., Vinciguerra, L., Bella, R., Vicari, E. and Malaguarnera, G. (2020). Acetyl-L-Carnitine in Dementia and Other Cognitive Disorders: A Critical Update. Nutrients, [online] 12(5), p.1389. doi:10.3390/nu12051389.
  15. Talenezhad, N., Mohammadi, M., Ramezani-Jolfaie, N., Mozaffari-Khosravi, H. and Salehi-Abargouei, A. (2020). Effects of l-carnitine supplementation on weight loss and body composition: A systematic review and meta-analysis of 37 randomized controlled clinical trials with dose-response analysis. Clinical Nutrition ESPEN, [online] 37, pp.9–23. doi:10.1016/j.clnesp.2020.03.008.
  16. Bloemendaal, M., Froböse, M.I., Wegman, J., Zandbelt, B.B., van de Rest, O., Cools, R. and Aarts, E. (2018). Neuro-Cognitive Effects of Acute Tyrosine Administration on Reactive and Proactive Response Inhibition in Healthy Older Adults. eneuro, [online] 5(2), pp.ENEURO.0035-17.2018. doi:10.1523/eneuro.0035-17.2018.
  17. ELDerawi, W., Naser, I., Taleb, M. and Abutair, A. (2018). The Effects of Oral Magnesium Supplementation on Glycemic Response among Type 2 Diabetes Patients. Nutrients, [online] 11(1), p.44. doi:10.3390/nu11010044.
  18. Zheng, J., Zheng, S., Feng, Q., Zhang, Q. and Xiao, X. (2017). Dietary capsaicin and its anti-obesity potency: from mechanism to clinical implications. Bioscience Reports, [online] 37(3). doi:10.1042/bsr20170286.
  19. Mesquita, T.R.R., de Jesus, I.C.G., dos Santos, J.F., de Almeida, G.K.M., de Vasconcelos, C.M.L., Guatimosim, S., Macedo, F.N., dos Santos, R.V., de Menezes-Filho, J.E.R., Miguel-dos-Santos, R., Matos, P.T.D., Scalzo, S., Santana-Filho, V.J., Albuquerque-Júnior, R.L.C., Pereira-Filho, R.N. and Lauton-Santos, S. (2017). Cardioprotective Action of Ginkgo biloba Extract against Sustained β-Adrenergic Stimulation Occurs via Activation of M2/NO Pathway. Frontiers in Pharmacology, [online] 8. doi:10.3389/fphar.2017.00220.
  20. Kaur, S., Sharma, N. and Nehru, B. (2017). Anti-inflammatory effects of Ginkgo biloba extract against trimethyltin-induced hippocampal neuronal injury. Inflammopharmacology, [online] 26(1), pp.87–104. doi:10.1007/s10787-017-0396-2.
  21. Ellulu, M.S., Patimah, I., Khaza’ai, H., Rahmat, A. and Abed, Y. (2017). Obesity and inflammation: the linking mechanism and the complications. Archives of Medical Science, [online] 4, pp.851–863. doi:10.5114/aoms.2016.58928.
  22. Santos-Gallego, C.G. and Juan José Badimón (2014). Niacin for Reduction of Cardiovascular Risk. [online] ResearchGate. Available at:
  23. Stach, K., Stach, W. and Augoff, K. (2021). Vitamin B6 in Health and Disease. Nutrients, [online] 13(9), p.3229. doi:10.3390/nu13093229.
  24. Li, J., Yin, L., Wang, L., Li, J., Huang, P., Yang, H. and Yin, Y. (2019). Effects of vitamin B6 on growth, diarrhea rate, intestinal morphology, function, and inflammatory factors expression in a high-protein diet fed to weaned piglets1. Journal of Animal Science, [online] 97(12), pp.4865–4874. doi:10.1093/jas/skz338.
  25. Sangle, P., Sandhu, O., Aftab, Z., Anthony, A.T. and Khan, S. (2020). Vitamin B12 Supplementation: Preventing Onset and Improving Prognosis of Depression. Cureus. [online] doi:10.7759/cureus.11169.
  26. Yang, X., Wang, H., Huang, C., He, X., Xu, W., Luo, Y. and Huang, K. (2017). Zinc enhances the cellular energy supply to improve cell motility and restore impaired energetic metabolism in a toxic environment induced by OTA. Scientific Reports, [online] 7(1). doi:10.1038/s41598-017-14868-x.


Mitchelle Morgan is a health and wellness writer with over 10 years of experience. She holds a Master's in Communication. Her mission is to provide readers with information that helps them live a better lifestyle. All her work is backed by scientific evidence to ensure readers get valuable and actionable content.


Kathy Shattler, MS, RDN
Medical Reviewer
Kathy Shattler has been a Registered Dietitian for over 25 years and currently runs her own Telehealth Clinic while freelance writing in her spare time. She graduated with a Master of Science degree in Human Nutrition from Michigan State University and has a plethora of experience in both clinical nutrition as well as public health. She has been deemed a trailblazer in her profession and continues to strive for excellence in public health education in integrative medicine and in her professional writing career.

Help us rate this article

Thank you for your feedback

Keep in touch to see our improvement