Phentermine Reviews: Efficacy & Side Effects

A doctor’s assessment of potential weight loss and possible side effects is important, but many users also want to hear about other patientsphentermine reviews and results

Learn more about real user experiences with this medication by reading through some of the phentermine testimonials below.

What Is Phentermine?

Phentermine is a prescription weight loss medication used to help overweight and obese patients lose weight.

As a central nervous system stimulant, it suppresses appetite and boosts fat burning by creating a biological response similar to “fight or flight” ( 1 ).

It’s typically used short-term, in conjunction with a low-calorie diet and exercise, for people who are significantly overweight or obese.

Does Phentermine Work?

The effectiveness of phentermine has been studied in multiple clinical trials. For instance, a 2016 systematic review published in the Journal of Obesity & Weight Loss Therapy analyzed several studies on phentermine and found that it led to significant weight loss when compared to a placebo. It was found to be particularly effective in the short term (a few weeks to months).

However, the long-term effectiveness of phentermine is less clear. The drug is typically recommended for short-term use because it can have side effects, and its impact on weight loss seems to decrease over time.

What Side Effects Does Phentermine Have?

Phentermine can cause a range of side effects, from mild to potentially fatal, making it crucial to be aware of the risks before starting treatment.

Severe side effects mainly include serious conditions such as Primary Pulmonary Hypertension (PPH), heart valve irregularities, mood changes, metabolic imbalances, drug reactions, and allergies.

Symptoms can be:

  • Chest pain
  • Irregular heartbeat
  • Lightheadedness
  • Shortness of breath
  • Edema
  • Slurred speech
  • Unusual behavior
  • Euphoria or depression
  • Signs of extremely high blood pressure.

Call 911 (emergency medical services) or go to a hospital right away if you notice any of these symptoms while taking phentermine.

While severe side effects are infrequent, more common and less threatening side effects include dry mouth, insomnia, constipation, headache, fatigue, sexual side effects, menstrual changes, hair loss, nausea, stomach pain, rash, acne, and diarrhea. An online poll revealed that over 80% of phentermine users had at least one occurrence of dry mouth.

User Experiences & Reviews

Users give phentermine an average rating of 4.2 out of 5 stars. This medication produces significant weight loss results, but many patients experience significant side effects. Learn about their individual success stories, challenges, and overall opinions of the weight loss medication below.


Happy happy: Five months and one week after starting phentermine I’m down 80 pounds. This was my first goal, and now that I’m here I think I’d like about 20 more pounds gone. I’m a size 6/8, which is good enough for me! The journey hasn’t been easy, but the results have been absolutely worth it. Phentermine has been a game changer and I feel more confident than ever.


I stopped taking the 37 mg because it was making my heart rate to go too high, my doctor told me to cut my dose to half. I’m starting the lower dose today and it didn’t made me feel as bad. So far, I’ve lost 24 pounds. It’s been a bit of a rollercoaster, but I’m optimistic about this new dosage. It’s all about finding the right balance and I believe I’m on the right track.


Due to complete hystorectomy and taking synthetic hormones, I gained about 46lbs. I lost 42lbs in 9 months (about 6 of constant use) and I am beyond happy. 🙂 I was size 12, now I am a 4 (again). Some side effects were hard to deal with, but I made it. It worked for me well with pauses in between (just taking half a pill, but never stopping) to rest the body from the side effects like dry mouth, mood swings, anxiety etc. Despite the occasional discomforts, Phentermine has been a key part of my journey to reclaim my health and happiness. Thank you Phentermine for giving me my life back, even if only for the summer!


Not For Everyone: I know the medicine is different for everyone. I’m have been taking it for 4 weeks. I’ve had two REALLY bad panic attacks and haven’t had them in years. Not liking the side effects at all. While Phentermine seems to work for some, it certainly isn’t the solution for everyone. My personal experience with it was rather unsettling, serving as a reminder to pay close attention to my body and its responses to medication. Think I will stop taking it.


I have been on Phentermine since the end of June, 2022. I lost 70 lbs. It definitely decreased my appetite significantly and helped me lose weight. The medication has been a great support in my weight loss journey, aiding in appetite suppression which has made it easier to control my eating habits. Its effectiveness is undeniable and I’m extremely satisfied with the results.


I was on capsules before at a lower dosage and did great! When my doctor increased the dosage it came in tablet form and I have been getting horrible headaches on and off for some time now. I just decided last night, after a horrible headache and nausea day, to stop taking the medication. The pharmacy told me I could not get capsules because my doctor prescribed it as tablets. So hopefully I will do fine on my own. It is a slow process but I have learned a lot. Good luck!


Used to be 199 now 159… took me 6 months. Now, I’m not taking the pill everyday and doing low carb/high protein and exercise. Phentermine gave me the initial boost I needed, but I’ve since transitioned into a healthier lifestyle that includes mindful eating and regular physical activity. Weight loss is a marathon, not a sprint, and I’m in it for the long haul. It’s difficult to lose after menopause, but slow and steady wins the race!


Initially, the side effects were challenging to handle, but adjusting the dosage helped significantly. I had terrible insomnia, hot flashes/sweating, and mood swings for 2 weeks before I asked for a lower dose. Now I’m doing much better. It’s been a rewarding experience to feel in control of my body again. I feel like I could do anything. Great stuff!

Brand Reviews

Users also share their opinions about specific phentermine brands, such as Adipex, Qsymia, or Acxion.


Adipex capsule and tablet

Adipex-P is the most popular brand of phentermine in the United States. These white and blue pills 37.5 milligrams of phentermine hydrochloride and are available in both capsule and tablet form.


Phentermine 8 mg

Lomaira is the lowest-available dose of phentermine. It is a brand-name tablet that contains just 8mg of phentermine hydrochloride per pill and can be easily split in half to provide an even smaller 4mg dose. 


Qsymia® capsules

Qsymia is a combined pill that contains two medications: phentermine hydrochloride (phentermine HCL) and topiramate extended-release (topiramate ER). While phentermine works as a stimulant to reduce appetite and boost fat burn, topiramate reduces cravings and makes food seem less appealing. Qsymia is approved for longer-term use than phentermine monotherapy, but also has a long list of potential side effects ( 5 ). 


Axcion® 30mg

Acxion is a Mexican brand of phentermine. It is sold as tablets, capsules, and extended-release tablets and is available in two different doses: 15mg and 30mg. Acxion is the most popular brand of phentermine in Mexico, and 30mg is the most common dose. 


Sentis® capsules

Sentis is a Chilean brand of phentermine. Prescription appetite suppressants are more common than ever in Chile, and Sentis is one of the most popular brands. These capsules are available in two doses, 18.75 mg, and 37.5 mg, but are only sold under a doctor’s prescription. Depending on individual dosage instructions, Sentis is taken 1-2 times per day. 


Terfamex® 15mg capsules

Terfamex is another popular Mexican brand of phentermine weight loss pills. It is available in three different doses – 15, 30, and 37.5 mg – and in two separate forms: capsules and orally disintegrating tablets (ODT). Terfamex is sold in Mexico, Venezuela, Peru, Colombia, Panama, and Argentina. It may be taken either once or twice per day, depending on prescribing instructions.

Phen Caps

Phen Caps capsules

Phen Caps is a herbal supplement that harnesses the power of nine natural ingredients to promote weight loss. Similar to phentermine, these capsules suppress appetite and boost energy to help users lose weight faster and easier. However, unlike phentermine, Phen Caps do not require a doctor’s prescription and are available online. More, this supplement does not cause any of the unpleasant side effects commonly associated with phentermine weight loss pills.


Phentermine has proven short-term benefits but has unclear long-term results as well as potentially dangerous side effects. User reviews indicate mixed experiences, with some users experiencing significant weight loss and others discontinuing due to side effects.

It is worthwhile considering as well reviews of specific Phentermine brands and herbal alternatives in order to find the best weight loss solution for your use case.

Back to Phentermine Reviews and Results

  1. National Center for Biotechnology Information. (2019, May 04). Phentermine, CID=4771.
  2. Teva Pharmaceuticals USA, Inc. (2017, March). Highlights of Prescribing Information.
  3. (2019). Phentermine Hydrochloride: Oral capsule.
  4. KVK Tech, Inc. (2018). Lomaira | Why wait to lose weight?
  5. VIVUS, Inc. (2014, September). Medication Guide: Qsymia® (Kyoo sim ee’ uh) (phentermine and topiramate extended-release) Capsules CIV.