Phentermine vs Qsymia: better alone or together? (updated)

January 9, 2024 |

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Qsymia is clearly the winner here because it is basically a stable phentermine combination therapy you may pursue in the long term. However, since Qsymia is a combination of two drugs, greater caution applies to its use as well.

Then which one is the better of the two?

Both Qsymia and phentermine suppress hunger and work in basically in the same way. However, because Qsymia has additional drug topiramate in its formulation, so it poses a greater risk-to-benefit ratio to the user.

Thus, phentermine is the preferred drug in most cases, but Qsymia might be the preferred prescription for individuals with the least contraindications.

In this article, you will become aware of the benefits, safety, user reviews, and cost of Qsymia and phentermine.

I will also highlight the pros and cons of these two diet pills so it is easier for you to skim through the content of this article.

So, let’s dive into the details without any further delay.

Phentermine vs. Qsymia – A Detailed Comparison

A Quick Overview of Qsymia and Phentermine

Phentermine formula

Phentermine and Qsymia are appetite suppressants that are prescribed in combination with some dietary modifications and exercise to promote weight loss in obese individuals.

However, in contrast to phentermine, which is a single drug, Qsymia is an extended-release combination by Vivus, Inc.

It is a medicine that combines the anorectic, phentermine-HCl, and an antiepileptic, topiramate extended-release capsule.

The conditions for prescribing both phentermine and Qsymia are the same. And they are prescribed to individuals with an initial BMI of 30 kg/m2 or greater. Or if the patient has an initial BMI of 26 kg/m2 and is co-morbid with diseases like controlled hypertension (high blood pressure), diabetes, and abnormal lipid levels.

Qsymia is available in four doses with varying concentrations of phentermine and topiramate in the following ratios, 3.75 mg/23 mg, 7.5 mg/46 mg, 11.25 mg/69 mg, and 15 mg/92 mg. It is taken once daily, either with or without food.

Phentermine is available in 4 dosage forms, namely 8 mg, 15 mg, 30 mg, and 37.5 mg.

The lower dosages like 8mg or 4 mg (half tablet) are recommended three times a day, 30 minutes before breakfast.

However, the higher dosages like 15 mg, 30 mg, and 37.5 mg can be taken only once a day, either before or after breakfast.


Phentermine primarily works to suppress appetite and gives an energy boost.

On the other hand, a single dose of Qsymia suppresses hunger and cravings throughout the day. Moreover, it is approved for long-term use.

Verdict: Qsymia has the edge in that it allows extensive therapy. Otherwise, both phentermine and Qsymia have a similar benefit in appetite suppression.

Safety of Phentermine and Qsymia

FDA approval

The good news is that both phentermine and Qsymia are FDA-approved anti-obesity treatments. Phentermine gained the initial FDA approval in 1959, and Qsymia got approved on July 17, 2012.

The difference, however, lies in the duration of treatment for which they got approved. Phentermine is approved only for short-term treatment and can be taken for at most 12 weeks. Whereas, Qsymia is an effective long-term treatment for obesity that can be pursued for over 6 to 12 months.

However, both phentermine and Qsymia have the potential for misuse. Thus, phentermine is regulated under Schedule IV of the Controlled substances act. And since Qsymia contains phentermine, so it is also a Schedule IV controlled substance.


Qsymia has phentermine in it, so its safety information is very much identical to the safety information of phentermine.

FDA classifies phentermine in the pregnancy category X, which means that it poses a high risk of harm to the fetus. Thus, both these drugs are not suitable if you are trying to conceive, have already conceived, or are a breastfeeding woman.

Moreover, studies have evaluated the safety of these drugs in adults above 16 years of age. Thus, they are not recommended for younger age groups.

Also, it is better to avoid taking these drugs late in the evening as they may cause insomnia.

Drug Contraindications

Phentermine has 170 drug interactions. Of these, 42 are major interactions, 126 are moderate, and 2 minor interactions. It may also cause adverse reactions if prescribed to people with 17 different diseases.

On the other hand, Qsymia may react with 387 drugs and cause 145 major reactions, 239 moderate, and 3 minor drug interactions. Moreover, it is not suitable for patients with about 26 different diseases.

For instance, these obesity treatments are not recommended for individuals with glaucoma or thyroid problems (hyperthyroidism). Nonetheless, you should always communicate your underlying illnesses like kidney, liver, and cardiovascular disease to your doctor so that they can advise the prescription of both phentermine and Qsymia accordingly.

Your doctor may not recommend these drugs for treatment if you are allergic to phentermine or other sympathomimetic amines or have a history of drug abuse. Additionally, Qsymia is to be avoided if you are also allergic to topiramate.

Moreover, your doctor may recommend against phentermine or Qsymia if you have taken monoamine oxidase inhibitors (MAOIs) inhibitors in the past 14 days because it may cause your blood pressure to shoot up.

Qsymia has been shown to decrease the efficacy of oral contraceptives as well.

Phentermine’s side effects

Discontinuing phentermine has been associated with symptoms like fatigue and depression.

Phentermine’s commonly reported side effects during treatment are mild as compared to Qsymia.

For instance, its impact on the nervous system can lead to fatigue or dizziness. Users also report psychological effects like anxiety and depression.

Its effect on the gastrointestinal system may cause dry mouth, nausea, constipation, etc.

Or you may get hives, rash, and headaches.

In rare cases, it may also cause more severe side effects like heart valve defects or primary pulmonary hypertension.

Qsymia’s side effects

If you quit Qsymia, besides the phentermine withdrawal effects, the topiramate in this combination may also cause the onset of seizures.

There is a long list of side effects caused by Qsymia during treatment, which may affect nearly all the body systems.

The most commonly reported side effects on the nervous system include headache and pins and needle sensation on the body.

Users also report psychological side effects like anxiety, depression, and irritability.

Your metabolism might also get affected, which may cause different electrolyte imbalances and decreased appetite.

Qsymia may increase serum creatine levels, which can also cause adverse effects on the kidney.

Most users complain of side effects related to the cardiovascular system, such as heart palpitations and elevated blood pressure.

Moreover, Qsymia puts increasing pressure on the eye; consequently, users mostly complain of dry eye, blurred vision, and eye pain.

Gastrointestinal side effects like constipation and dry mouth are also commonly reported.

In case your genitourinary tract gets affected, it may cause urinary tract infection or other illnesses.

Your immunity might get compromised with this drug, and there are reports of Qsymia causing influenza.

The effect of Qsymia on the musculoskeletal and respiratory systems may manifest symptoms like neck and back pains or upper respiratory tract infection, respectively.

Other side effects you may look out for are hair fall, rash, etc.

Verdict: Phentermine is a safer option compared to Qsymia. The reason is that it has fewer drug contraindications and a shorter list of side effects.

User reviews

Phentermine rates 8.7 out of 10 based on the average ratings given by 2,918 users on

There are 84% positive reviews and 5% negative reviews regarding it on the website.

You may lose about 3-5 pounds every month on phentermine.

Most positive reviews have reported significant weight loss progress.

Users seem extremely satisfied with the increase in their energy levels because it enabled them to fulfill different chores and spend more time at the gym.

Most negative reviews included complaints of dependency and psychological symptoms like depression or their weight loss progress being stuck at a phentermine plateau.

Compared to this, Qsymia has an average rating of only 7.8 out of 10 based on only 550 user ratings on

72% of users have written positive reviews, whereas 14% of users have written negative reviews regarding it on the website.

Both negative and positive reviews have reported facing the same kind of side effects like dry mouth, depression, or tingling in hands and feet.

Verdict: Phentermine is clearly the more trusted and preferred diet pill among users based on the reviews and ratings.

Cost of Qsymia and Phentermine

A 30-day supply (30 capsules) of the lowest dose of Qsymia, which is 7.5mg/46mg comes at an average retail price of $233.85.

And 30 capsules of its highest dose, that is 15mg/92mg, cost around $248.04.

Moreover, there is also a scheme of paid home delivery from pharmacies that you can check on this website.

Compared to this, you can get 30 tablets of the highest dose of phentermine, which is 37.5 mg, for $36.5 only.

Verdict: Phentermine is way more cost-effective than Qsymia as it has low-cost generic forms available.

Pros and cons

Phentermine Pros

  • It suppresses appetite, reduces cravings, and boosts energy
  • It is FDA approved
  • It can be prescribed with comorbidities
  • Its higher doses can be taken both with and without food
  • Its higher doses can be taken once daily
  • It is more cost-effective

Phentermine Cons

  • It is a short-term treatment
  • It has to be combined with diet and exercise
  • Lower doses are recommended about three times a day
  • It can cause trouble sleeping if taken late
  • It is a Schedule IV drug
  • It cannot be bought online
  • Lower doses have to be taken three times a day
  • It is available only on prescription
  • It has 170 drug interactions
  • It has 17 disease interactions

Qsymia Pros

  • It is a long-term treatment
  • It is FDA approved
  • It can be prescribed for people co-morbid with certain diseases
  • It is not compulsory to take it with food
  • It is taken only once a day
  • It is available online

Qsymia Cons

  • It has no cost-effective generic versions
  • It may cause insomnia when taken late
  • It only supports modifications in diet and physical activity
  • It may cause seizures and phentermine side effects on abrupt cessation
  • It should not be taken if allergic to sympathomimetic amines and topiramate
  • It is a Schedule IV controlled substance
  • It can only be bought by prescription
  • It can interact with a total of 387 drugs
  • It is reported to have 26 disease interactions

Verdict: Phentermine and Qsymia have their equal share of pros. But in terms of severity of cons, phentermine seems to have a fewer disease and drug interactions.

Also read: Saxenda vs Phentermine: Which is better?

FAQs on Qsymia vs Phentermine

Is phentermine as effective as Qsymia?

Yes, both phentermine and Qsymia have similar effects on appetite suppression.

Can you take Qsymia and phentermine together?

No, Qsymia already combines phentermine along with topiramate in its formulation. Taking Qsymia and phentermine together may lead to overdosage and adverse reactions.

How many mg of phentermine is in Qsymia?

Qsymia comes in four doses, and the lowest dose contains 3.75 mg of phentermine. Other pills may have 7.5 mg pr 11.25 mg of phentermine. And the highest dose has 15 mg of phentermine combined with topiramate.

How fast do you lose weight on Qsymia?

Qsymia starts working in the body as soon as you start taking it. According to a clinical trial, you may lose around 6.7% to 8.9%  of your initial body weight after one year of treatment.

Does Qsymia work better than phentermine?

Yes, Qsymia is considered a more potent weight loss medicine than only phentermine. According to 28-week comparative research, the Qsymia combination therapy induced more significant weight loss even at lower doses than phentermine and topiramate monotherapies.


In a nutshell, Qsymia has long-term treatment benefits. On the other hand, phentermine is more suitable for short-term treatment because it has an established efficacy profile and can be prescribed to the majority population.

However, both these drugs are not recommended during pregnancy and nursing days.

The topiramate in Qsymia counters phentermine’s stimulation effects, which reduces its risk of dependency.

On the contrary, phentermine is the more affordable option, and its withdrawal side effects are also less scary, as terminating Qsymia abruptly may cause seizures.

Remember, always discuss your medical history with your doctor when he proposes prescribing any diet pills, including phentermine and Qsymia.

Moreover, the safety of diet pills is only established for ages above 18 years of age, so avoid them if you fall in the younger age group.

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