What is the equivalent dose of Adderall (amphetamine and dextroamphetamine) to Vyvanse (lisdexamfetamine) 50 mg?

Vyvanse 50 mg to Adderall Dose Equivalence

Vyvanse (lisdexamfetamine) 50 mg is approximately equivalent to 20 mg of Adderall (mixed amphetamine salts).

Pharmacological Basis for Equivalence

Vyvanse (lisdexamfetamine) is a prodrug that is enzymatically converted to dextroamphetamine in the bloodstream after ingestion. This conversion process is important to understand when determining dose equivalence:

• Vyvanse 50 mg contains 50 mg of lisdexamfetamine dimesylate, which is equivalent to 28.9 mg of lisdexamfetamine base 1
• When metabolized, this yields approximately 17.3 mg of dextroamphetamine 1
• Adderall contains a 3:1 ratio of dextroamphetamine to levoamphetamine 2
• Taking into account the potency differences between the isomers, 20 mg of Adderall provides a roughly equivalent amount of active amphetamine as 50 mg of Vyvanse

Pharmacokinetic Differences

While the total exposure (AUC) of dextroamphetamine is similar between equivalent doses of Vyvanse and Adderall, there are important pharmacokinetic differences:

• Vyvanse has a longer time to peak concentration (Tmax) - approximately 3.5 hours for the active dextroamphetamine component compared to Adderall's faster onset 1
• Vyvanse provides approximately 12-14 hours of clinical effect due to its prodrug mechanism 3
• Adderall immediate-release typically provides 4-6 hours of effect, while Adderall XR provides about 12 hours through its dual-release bead technology 2

Clinical Considerations

When switching between these medications, consider:

• The conversion ratio is approximately 2.5:1 (Vyvanse:Adderall)
• Vyvanse has a more gradual onset and potentially smoother effect profile due to its prodrug mechanism 4
• Adderall contains both dextroamphetamine and levoamphetamine, which may result in slightly different side effect profiles for some patients
• The American Academy of Child and Adolescent Psychiatry does not support combining different stimulant medications due to potential increased side effects 5

Dosing Algorithm

When converting from Vyvanse to Adderall:

1. Divide the Vyvanse dose by 2.5 to get the approximate Adderall equivalent
2. Round to the nearest available Adderall dosage strength
3. Monitor for efficacy and side effects, adjusting as needed

For Vyvanse 50 mg specifically:

• 50 mg ÷ 2.5 = 20 mg Adderall

Cautions

• Individual response may vary based on metabolism, body weight, and other factors
• Careful monitoring is required when switching between stimulant medications
• Both medications have similar contraindications including glaucoma, cardiovascular disease, hyperthyroidism, and concurrent MAOI use 5

This conversion ratio provides a reasonable starting point, but clinical response should be the ultimate guide for optimal dosing.