Phentermine and Adderall are both central nervous system (CNS) stimulants, but they are approved for very different medical conditions and carry distinct risk profiles [1.2.1, 1.3.5]. While they share a similar chemical structure to amphetamines, they are not interchangeable [1.8.1, 1.8.6]. Understanding their primary uses, mechanisms of action, and legal classifications is essential for safe and effective treatment.
What is Phentermine?
Phentermine is an FDA-approved prescription medication primarily used for short-term weight management in individuals with obesity (BMI ≥30) or who are overweight (BMI ≥27) with at least one weight-related comorbidity like controlled high blood pressure or diabetes [1.5.2, 1.5.4]. It is intended to be used for 12 weeks or less in conjunction with a reduced-calorie diet and exercise [1.4.2, 1.4.7].
Mechanism of Action
Phentermine works by stimulating the release of norepinephrine in the brain [1.3.7, 1.5.4]. This neurotransmitter helps to reduce hunger signals, suppressing appetite and leading to lower calorie consumption [1.3.7, 1.8.1]. It also increases energy levels, which can further aid in weight loss [1.8.4]. While it also has a minor effect on dopamine, its primary impact is on norepinephrine [1.8.1].
What is Adderall?
Adderall is the brand name for a combination of amphetamine and dextroamphetamine salts [1.3.2]. It is FDA-approved to treat Attention-Deficit/Hyperactivity Disorder (ADHD) in people aged 3 and older and narcolepsy, a sleep disorder causing excessive daytime sleepiness [1.3.2, 1.6.4]. Unlike phentermine, Adderall can be prescribed for long-term use [1.4.2].
Mechanism of Action
Adderall works by increasing the levels of two key neurotransmitters in the brain: dopamine and norepinephrine [1.3.7]. The increase in dopamine is associated with motivation and reward, while norepinephrine enhances alertness, attention, and focus [1.8.1]. This combined action helps to improve concentration and reduce impulsivity and hyperactivity in individuals with ADHD [1.8.1].
Core Differences: Phentermine vs. Adderall
The primary distinction lies in their approved uses: phentermine is for weight loss, and Adderall is for ADHD and narcolepsy [1.2.1]. Although both are stimulants, their chemical structures and effects on brain chemistry differ. Phentermine primarily targets norepinephrine to suppress appetite, while Adderall has a more potent effect on both dopamine and norepinephrine to improve focus [1.8.1].
Another critical difference is their legal classification by the Drug Enforcement Administration (DEA). Adderall is a Schedule II controlled substance, indicating a high potential for abuse, dependence, and addiction [1.4.2]. Phentermine is a Schedule IV controlled substance, meaning it has a lower, but still present, potential for abuse and dependence [1.2.1, 1.4.2]. This difference impacts prescription regulations; for instance, Adderall prescriptions typically cannot be refilled, requiring a new prescription each time [1.4.2].
| Feature | Phentermine | Adderall |
|---|---|---|
| Primary Use | Short-term weight loss [1.2.1] | ADHD, Narcolepsy [1.2.1] |
| Active Ingredient | Phentermine Hydrochloride [1.8.3] | Amphetamine/Dextroamphetamine salts [1.3.2] |
| Mechanism | Primarily increases norepinephrine [1.8.1] | Increases dopamine and norepinephrine [1.3.7] |
| DEA Schedule | Schedule IV [1.2.4] | Schedule II [1.2.4] |
| Duration of Use | Short-term (≤12 weeks) [1.4.2] | Long-term [1.4.2] |
| Abuse Potential | Lower potential for abuse [1.4.2] | High potential for abuse [1.4.3] |
Off-Label Uses
Due to their stimulant properties, both drugs are sometimes used off-label—for purposes not approved by the FDA.
- Phentermine for ADHD: Some prescribers may use phentermine off-label for ADHD because its effect on norepinephrine can help with focus [1.5.1]. However, there are no robust clinical trials to support its effectiveness for this use, and more proven medications like Adderall and Ritalin are considered safer and more effective options [1.5.3, 1.5.4].
- Adderall for Weight Loss: Weight loss is a common side effect of Adderall due to its appetite-suppressing effects [1.6.5]. However, it is not approved for this purpose [1.6.4]. Using Adderall for weight loss is considered misuse and can be dangerous, leading to tolerance, dependence, and serious cardiovascular and psychological side effects [1.6.1, 1.6.3]. Any weight lost is often regained after stopping the medication [1.6.1].
Side Effects and Risks
Both medications share common stimulant side effects, including insomnia, dry mouth, increased heart rate, and elevated blood pressure [1.2.1]. However, they also have distinct risk profiles.
- Phentermine is more associated with cardiovascular issues like pulmonary hypertension (high blood pressure in the lungs) [1.2.1]. It should not be used by people with glaucoma or hyperthyroidism [1.2.2].
- Adderall carries a boxed warning from the FDA, the most severe type, regarding its high potential for abuse and the risk of sudden death and serious cardiovascular events with misuse [1.4.3]. It can also worsen underlying mental health conditions, slow growth in children, and trigger seizures [1.2.1].
Conclusion
While phentermine and Adderall are both stimulants, they serve different therapeutic purposes and are not interchangeable. Phentermine is a short-term solution for weight loss by suppressing appetite, with a lower risk of dependence [1.2.6, 1.4.2]. Adderall is a long-term treatment for ADHD and narcolepsy that improves focus and attention but carries a significantly higher risk of abuse and addiction [1.2.6, 1.4.2]. The decision to use either medication must be made with a healthcare provider who can weigh the benefits against the substantial risks, especially concerning their off-label use.
For more information on stimulant medications, a valuable resource is the National Institute on Drug Abuse (NIDA).
