Which FDA‑approved amphetamine (e.g., methamphetamine [Desoxyn], mixed amphetamine salts [Adderall], dextroamphetamine [Dexedrine/DextroStat], lisdexamfetamine [Vyvanse]) is most potent at its approved dosing?

Amphetamine Potency at FDA-Approved Doses

At FDA-approved therapeutic doses, dextroamphetamine (Dexedrine) and mixed amphetamine salts (Adderall) are the most potent amphetamines, requiring only 2.5 mg starting doses compared to methylphenidate's 5 mg, reflecting approximately twice the milligram-per-milligram potency. 1

Comparative Dosing Framework

The established dosing guidelines reveal clear potency differences:

Starting Doses

• Dextroamphetamine/Mixed Amphetamine Salts (DEX/AMP): 2.5 mg 1
• Lisdexamfetamine (Vyvanse): 20-30 mg (prodrug requiring conversion) 2
• Methylphenidate (MPH): 5 mg 1

Maximum Daily Doses

• Dextroamphetamine/Mixed Amphetamine Salts: 40 mg total daily 1
• Lisdexamfetamine: 70 mg total daily 2, 3
• Methylphenidate: 60 mg total daily 1

Potency Analysis

The 2:1 dosing ratio between amphetamines and methylphenidate demonstrates that amphetamines are approximately twice as potent milligram-for-milligram. 1 Titration schedules confirm this: methylphenidate increases by 5-10 mg increments while amphetamines increase by 2.5-5 mg increments 1.

Lisdexamfetamine Considerations

Lisdexamfetamine requires special consideration as a prodrug. While its starting dose appears higher (20-30 mg), it must be enzymatically converted to dextroamphetamine in the blood 2, 4. The prodrug formulation results in:

• Lower peak plasma concentrations (Cmax)
• Extended time to maximum concentration (Tmax)
• Reduced inter- and intra-individual variability 4

The therapeutic duration of lisdexamfetamine extends to 13-14 hours, longer than any other long-acting formulation, but this reflects pharmacokinetic properties rather than inherent potency. 4

Clinical Implications

Side Effect Profile

Amphetamines (DEX/AMP) produce greater problematic effects on appetite and sleep compared to methylphenidate, consistent with their longer excretion half-lives and higher potency. 1 This is a critical consideration when selecting initial therapy.

Age-Related Pharmacokinetics

Children exhibit shorter plasma half-lives (7 hours) compared to adults (10-12 hours) for amphetamines 5. Body weight is a fundamental determinant of plasma concentrations, though the 2:1 potency ratio versus methylphenidate remains consistent across age groups 5.

Common Pitfalls

1. Do not assume lisdexamfetamine's higher milligram dosing indicates lower potency - it is a prodrug requiring conversion to active dextroamphetamine
2. Avoid direct milligram-to-milligram conversions between methylphenidate and amphetamines - use the established 2:1 ratio (5 mg MPH ≈ 2.5 mg AMP)
3. Children weighing <25 kg should not receive single doses >10 mg DEX/AMP or >15 mg MPH 1

Monitoring Requirements

All amphetamines require:

• Baseline and ongoing blood pressure/pulse monitoring 1
• Weight monitoring at each visit (appetite suppression is dose-related) 6
• Quarterly cardiovascular assessment in adults 1

The evidence consistently demonstrates that among FDA-approved amphetamines, dextroamphetamine and mixed amphetamine salts are most potent at approved doses, requiring half the milligram dosing of methylphenidate for equivalent therapeutic effect. 1