Phentermine vs Adderall: (weight loss, dosage, energy)

January 8, 2024 |

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This article will help you find and understand the differences between phentermine vs. Adderall.

Just found that you can use both these drugs for similar purposes, and now you are surfing the internet to decide on the better one of the two in terms of cost and effectiveness.


I’ve got all the answers for you.

Both phentermine and Adderall are indeed different versions of amphetamine, and therefore they are used off-label for each other’s primary functions. But using them outside their reported potential does not guarantee the results you are looking for.

This article will fill you in on the efficacy, side effects, and cost of these two treatments so that you can understand why they are sold under different names and for treating different ailments.

So, keep reading to find out the details.

Phentermine vs Adderall – Overview

Phentermine is an FDA-approved anorectic and sympathomimetic drug prescribed to aid weight loss if you have a BMI over 30 or over 27.

It works by suppressing the appetite and by increasing the resting energy expenditure. It is sold under the names Adipex-P, Atti-Plex P, and Lomaira.

On the other hand, although Adderall is not an FDA-approved drug, it is prescribed to improve Attention-Deficit Hyperactivity Disorder (ADHD) and narcolepsy symptoms.

It is a central nervous system stimulant that may help to enhance focus and attention and reduce hyperactivity and impulsiveness.

‘Adderall’ is the generic name for a mixture of the two stimulants, namely dextroamphetamine, and amphetamine salt.

Nonetheless, both these drugs are used off-label as effective substitutes for each other’s functions.

But even if phentermine and Adderall can be used for both weight loss and ADHD, there are still differences in their potential for countering each condition.

Phentermine and Adderall Difference

Phentermine is a weight loss drug while Adderall is used to treat ADHD. though they are both stimulants, they have different effects on the body. Phentermine suppresses the appetite while Adderall increases focus and energy.

So, keep reading to find out how they vary in effectiveness, side effects, and price.

1. Efficacy

Phentermine is an active ingredient that is available in different brands, whereas Adderall is itself the specific brand, so the criterion for comparison is a bit loose here.

Moreover, both phentermine and Adderall were initially designed by scientists with different treatment goals in mind.

But their potential benefit as alternative treatments for ADHD and obesity has been discovered over time.

So, here is how different clinical trials have supported the effectiveness of the two drugs in weight loss and ADHD.

Phentermine vs. Adderall – weight loss

This clinical trial evaluated the efficacy of the optimum dose of 37.5 mg phentermine HCl on the weight loss outcome of participants.

It reported that more than 80% (87.5%) of the participant lost 5% or more of their weight, and more than half of them (58.3%) lost 10% or more of their weight compared to the placebo during the 12-week trial.

Stimulant drugs like Adderall show an added effect of reducing appetite and causing fat loss which is why it is sometimes exploited off-label to induce weight loss.

But I found that only user experience vouches for Adderall’s weight-loss potential, and there is no solid scientific proof to support the idea.

Many celebrities have been seen flaunting the ‘Adderall speed diet’ on television. NBC News reported that the television producer Amanda F. claims that Adderall has helped her maintain a size 6, and previously her size used to fluctuate between 14 and 2.

In their article, NBC News also quoted a neurology expert Paul Thompson from UCLA David Geffen School of Medicine, to explain why Adderall may cause weight loss.

And according to him, Adderall causes an imbalance of the three chemicals epinephrine, norepinephrine, and dopamine by stimulating their release and preventing their uptake in the brain, which may contribute to its weight loss potential. BBC has also reported that the singer ‘Lilly Ellen’ got addicted to Adderall for its weight loss potential.

As for now, there is no significant research to prove Adderall’s potential in causing weight loss.

And phentermine has both the edge of being the FDA-approved weight loss pill and has abundant research to prove its weight-loss potential, so in this case, it is, without a match, the champion drug in the phentermine vs. Adderall battle.

Phentermine vs Adderall – ADHD

This placebo-controlled clinical trial measured the effectiveness of Adderall among different age groups of both genders and found that the efficacy rates were similar in both males and females but varied among the three age groups included in the study.

The overall efficacy rate in 143 participants was 49%, whereas it was 60% in the age group of 5 to 7 years, 71% in the age group of 8 to 9 years, and 48% for children aged 10 or older.

Moreover, Adderall was also proved to be the best among the clinical trials that compared its efficacy with other candidate drugs for ADHD.

For instance, this clinical trial showed that Adderall’s doses were more potent and showed greater improvement than similar doses of the drug Ritalin.

This case report is the earliest and the only scientific evidence I found to back the use of phentermine in ADHD patients.

It reports the case of a 4-year-old boy who was diagnosed with ADHD and underwent treatment with phentermine hydrochloride. He showed signs of improvement, and it was annotated to the potential of phentermine to stimulate the central nervous system and produce dopamine, similar to other psychostimulants prescribed for ADHD.

Since there is no substantial scientific evidence on phentermine’s use for ADHD and neither are there any stats available to judge its efficacy rate so, Adderall should be the preferred choice in your phentermine vs. Adderall query in the case of ADHD.

2. Phentermine vs Adderall – Side effects

Since both Adderall and phentermine are stimulant drugs, their side effects are somewhat identical.

But still, there are some differences as well, so let me introduce you to some potential adverse reactions that may occur when you are on their prescription.

Loss of appetite, gastrointestinal symptoms, and insomnia are the most common adverse effects observed with either a low or high dose of Adderall.

Headache is one side effect that may worsen with increasing its dosage. Some other reported side effects are anxiety, hallucinations, headache, dizziness, high blood pressure, uneven or rapid heart rate, changes in libido, etc.

Dry mouth and insomnia are two of phentermine’s most reported side effects.

Some other side effects that manufacturers warn of are gastrointestinal symptoms, vomiting, changes in libido, change in taste, high blood pressure, irregular heartbeat, dizziness, headaches, urticaria, mood changes, impotence, hypersensitivity (hives, itching, etc.).

Some of the common side effects of both drugs are gastrointestinal symptoms, headache, insomnia, high blood pressure, and changes in libido.

In contrast, dry mouth is one side effect specific to phentermine and hallucinations to Adderall.

3. Cost

The price of purchasing the two drugs varies depending on your location, the vendor, the grams of the tablet, and whether you have a discount or insurance covering your medical expenses.

According to, one unit of a 5 mg Adderall tablet costs $9.53 (with a discount), and its 100 pills cost around $953 in the US.

Whereas the price of one unit of a 37.5 mg phentermine tablet is $1.82 (with discount) and its seven tablets cost $13 in the US, as mentioned at

According to the prices, phentermine is cheaper than Adderall, but you can’t use them interchangeably without your doctor’s prescription.

Some insurance companies cover treatment costs of both obesity and mental health, so you may check up with them to offer some relief in your case.

Can you take phentermine and Adderall on the same day?

It is better that you don’t, but your doctor will guide you better in this regard.

Since both these drugs are basically different versions of amphetamine and stimulate your central nervous system so they may mess with your neurotransmitters and brain.

Both phentermine and Adderall are suspected to affect your heart, blood pressure, appetite, stomach, and sleep schedule and cause other side effects, so it is better to avoid taking them together without your doctor’s advice.

Your doctor may recommend different doses of the two drugs to prevent double dosing of amphetamine on the same day. Or he may adjust the gap between the two prescriptions by considering their half-lives.

According to, the half-life of phentermine is 20 hours, whereas the half-life of Adderall is 34 hours.

Can I take Adderall and Phentermine together?

Your doctor knows the answer to this question, so don’t refer to my verdict in this case.

But since you asked, I can tell you that according to, no drug interactions are reported between Adderall and phentermine.

However, since you moved down from the previous section, you might already know that both drugs are psychostimulants and have some common side effects, so you may suspect a more pronounced positive or negative outcome from taking the two drugs together.

Moreover, a user on Quora has reported that his urinalysis tested positive for Adderall after taking phentermine which indicates that both drugs have a similar structure, so taking them together may carry a risk of overdosing.

Phentermine or Adderall – Which is Better for energy?

Phentermine and Adderall are both central nervous system stimulants, so they can both be effective for increasing energy levels. However, they work in different ways.

Phentermine is an appetite suppressant, so it can help people to feel less tired by reducing the need for food. Adderall, on the other hand, increases levels of the neurotransmitters norepinephrine and dopamine, which can lead to increased alertness and energy.

So which one is better?

Well, it really depends on the individual.

Some people may find that Phentermine helps them to more easily avoid overeating and crashing from sugar highs, while others may find that Adderall keeps them more focused and motivated throughout the day.


To wrap it up, phentermine is the best choice for promoting weight loss, whereas Adderall is the better drug for improving ADHD.

Both these drugs lack safety and efficacy studies to support their use in conditions other than they are primarily designed for, so their non-standard benefit cannot be claimed with surety.

So, to clarify, weight loss is more of a collateral effect of Adderall, and phentermine’s potential to improve ADHD is just its concomitant benefit.

So, taking drugs only for their actual purpose should be your first choice for achieving optimum results.

And remember that self-medication is detrimental to your health, so always trust your doctor’s advice.

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