Phentermine vs. Adderall: Similarities & Differences

For the treatment of attention deficit hyperactivity disorder (ADHD), healthcare providers may prescribe medications to manage symptoms.

Adderall (dextroamphetamine/amphetamine or mixed amphetamine salts), is a commonly prescribed stimulant that is approved by the Food and Drug Administration (FDA) to help with symptoms of ADHD.

Phentermine is a generic prescription drug that is FDA-approved for weight loss when combined with diet and exercise. It may sometimes be prescribed off-label for ADHD. The active ingredient phentermine is available under various brand names, such as Lomaira and Adipex-P.

Adderall and phentermine are often compared since they are used for overlapping conditions.

However, these drugs are not interchangeable, and both carry notable differences, especially concerning dosing guidelines, age requirements, and potential side effects, that potential users should understand.

Understanding Phentermine

Phentermine is part of a drug class called anorectics (drugs used to expedite weight loss) and is chemically related to amphetamine, one of the active ingredients in Adderall.

It is a controlled substance classified as a Schedule IV drug, with some potential for abuse and dependence. It comes as tablets and extended-release (XR) capsules. When used for weight loss, it is safe for people ages 17 and older.

It is FDA-approved for short-term use (several weeks, generally up to 12 weeks) along with other measures, such as diet and exercise.

Generally, individuals must fit specific criteria to take phentermine and must have a body mass index (BMI) equal to or higher than 30 kilograms (kg) per meters squared (m²), meaning a person’s weight in kilograms divided by their height in meters squared (kg/m²).

Alternatively, users can have a BMI of 27 kg/m² or higher in addition to other risk factors, such as hypertension (high blood pressure), high cholesterol, and/or type 2 diabetes.

How It Works

Phentermine works by reducing appetite. At times, healthcare providers may prescribe phentermine off-label (using a drug for a condition for which it was not FDA-approved) for longer than it is FDA-approved.

Because phentermine is FDA-approved to be used for no longer than 12 weeks, using it for longer or intermittently (on and off) would be considered an off-label use.

Phentermine is also available as an ingredient in a medication called Qsymia. Qsymia contains two ingredients: phentermine and topiramate.

Qsymia is FDA-approved for chronic weight management in adults and adolescents 12 years and older who meet specific criteria.

Understanding Adderall

Adderall is a brand-name prescription medication available in immediate-release (IR) and XR formulations.

It's available in two formulations, as follows:

• Adderall IR tablets can treat ADHD or narcolepsy (a chronic neurological condition affecting how the brain controls sleep-wake cycles) in adults and children.
• Adderall XR capsules can treat ADHD in adults and children. However, Adderall XR is not FDA-approved to treat narcolepsy.

Adderall is part of a drug class called central nervous system (CNS) stimulants. And, like phentermine, it is a controlled substance, specifically classified as a Schedule II drug.

But unlike phentermine, Adderall carries a boxed warning since, as a Schedule II drug, it has a high potential for abuse and severe dependence.

For context, a similar drug to Adderall is Mydayis, a brand-name CNS stimulant that contains mixed amphetamine salts, the same ingredients as Adderall. It is an ER capsule for treating ADHD in adults and adolescents 13 years and older.

How It Works

Adderall works by increasing the number of certain substances in the brain that help with alertness, concentration, and focus.

ADHD medications like Adderall are prescribed as part of a treatment plan that includes other measures, such as therapy, educational intervention, and lifestyle changes.

Healthcare providers may prescribe Adderall off-label for some of the following uses:

• Weight loss
• Fatigue related to depression
• Stroke
• Traumatic brain injury (brain dysfunction due to an outside force, such as a violent blow to the head, a severe sports injury, or a car accident)
• Excessive daytime sleepiness due to obstructive sleep apnea (interrupted breathing during sleep due to throat muscles relaxing and blocking airflow to the lungs)
• Helping fatigue or improving mental alertness in people with multiple sclerosis (MS)
  

Dosing Comparison

Dosage forms and doses of these medications are as follows.

Phentermine

Orally administered phentermine is commonly given in the following ways:

• Capsules: 15 milligrams (mg), 30 mg, 37.5 mg
• Tablets: 8 mg (Lomaira), 37.5 mg

The usual dosage is 15 mg, 30 mg, or 37.5 mg by mouth once daily in the morning about two hours before breakfast.

Lomaira, however, contains a lower dose of phentermine. It is usually prescribed as one-half (4 mg) or one (8 mg) tablet by mouth three times daily, 30 minutes before meals.

Healthcare providers are advised to prescribe the lowest effective phentermine dose.

Adderall

Orally administered Adderall is commonly given in the following ways:

• Adderall IR: 5 mg, 7.5 mg, 10 mg, 12.5 mg, 15 mg, 20 mg, and 30 mg
• Adderall XR: 5 mg, 10 mg, 15 mg, 20 mg, 25 mg, and 30 mg

Standard dosing schedules for Adderall include:

• ADHD in children 3–5 years old: The starting dose is 2.5 mg daily. The healthcare provider may gradually increase the dose if needed.
• ADHD in adults and children 6 years and older: The starting dose is 5 mg once or twice daily. The healthcare provider may gradually increase the dose if needed. The maximum total daily dose is 40 mg.
• Narcolepsy: The dose will vary based on age and response to treatment. Generally, the dose is 5 mg to 60 mg per day (in divided doses).

The dosages of Adderall XR are:

• Children and adolescents ages 6–17: 10 mg once daily in the morning
• Adults: 20 mg once daily in the morning

Healthcare providers are advised to prescribe the lowest effective dose of these drugs.

Side Effects & Safety

As with all drugs, phentermine and Adderall have potential adverse effects.

Therefore, closely monitor yourself or a loved one for any emerging side effects, particularly symptoms that do not improve or continue to worsen.

Adderall carries a boxed warning, the most severe warning required by the FDA. The warning states that amphetamines, like Adderall, have a high potential for abuse, which can lead to dependency. Also, misusing Adderall can cause serious heart problems and/or sudden death.

Because of these risks, it's essential to talk with your healthcare provider about the benefits and risks before taking Adderall.

Phentermine

Common side effects associated with the use of phentermine include:

• Dry mouth
• Unpleasant taste in the mouth
• Stomach problems like vomiting, constipation, or diarrhea

Call your healthcare provider right away if you have serious side effects.

Serious side effects associated with the use of phentermine include the following:

• Increased blood pressure
• Palpitations (feeling like the heart is racing, pounding, or fluttering)
• Dizziness
• Difficulty sleeping
• Shortness of breath
• Angina (chest pain)
• Swollen legs and ankles

Adderall

Common side effects associated with the use of Adderall include the following:

• Nervousness
• Headache
• Changes in sex drive; erectile dysfunction (ED)
• Menstrual cramps
• Dry mouth
• Stomach problems like nausea, constipation or diarrhea
• Weight loss

Serious side effects associated with the use of Adderall include the following:

• Slowed or difficult speech
• Numbness or weakness of an arm or leg
• Seizures
• Tics (repeated, sudden, and uncontrollable twitching, movements, or sounds)
• Grinding of teeth
• Depression
• Hallucinations (seeing or hearing things that are not there)
• Agitation
• Mania (an abnormally excited or irritated mood)
• Blistering or peeling skin
• Hoarse voice

Because this medication may affect growth and weight gain, children who take Adderall or Adderall XR will be closely monitored as they physically develop.

Precautions

Phentermine and Adderall aren't safe for everyone, and each drug has a long list of contraindications (reasons not to take medication due to safety concerns), warnings, and potential drug interactions to consider.

Before taking one of these medications, be sure to speak openly with your healthcare provider and tell them about:

• Your allergies to medications
• Medical conditions you currently have
• Medical conditions you have previously had
• Your family medical history
• All of the medications you take, including prescription medicines, over-the-counter (OTC) drugs, and vitamins or supplements

This information will help your healthcare provider determine if one of these medications is safe and appropriate.

Phentermine and Adderall should be avoided in people with certain conditions or medical histories, including:

• People with a history of heart disease, including coronary artery disease, stroke, heart rhythm conditions, congestive heart failure (CHF), or hypertension
• People who take medication in the monoamine oxidase inhibitor (MAOI) drug class, and within 14 days of taking medication in this class
• People with a history of overactive thyroid
• People with a history of glaucoma
• People with a history of substance use disorder
• People who are pregnant or nursing
• People with known allergies to any ingredient in phentermine or Adderall

Summary

Phentermine and Adderall are two commonly prescribed medications. Phentermine is FDA-approved as a weight loss drug for people who have obesity, while Adderall is FDA-approved to treat and manage ADHD and narcolepsy.

Uses can overlap. For instance, phentermine is sometimes prescribed off-label to treat and manage ADHD, while Adderall, under certain circumstances, is sometimes prescribed for weight loss.

These drugs vary regarding dosing, age requirements for particular uses, and potential side effects. Both medications are controlled substances and come with a risk of abuse and dependency.

Your healthcare provider will decide the best treatment for you based on many factors, including your medical history.