What is the dose equivalent of 40mg Vyvanse (Lisdexamfetamine) to Adderall IR (Amphetamine)

Vyvanse to Adderall IR Dose Conversion

For a patient taking 40mg Vyvanse, the equivalent dose of Adderall IR is approximately 16mg, based on a conversion ratio of 2.5:1 (Vyvanse:Adderall).

Conversion Algorithm

The established conversion factor is 2.5:1 (Vyvanse:Adderall), meaning 40mg Vyvanse converts to approximately 16mg Adderall IR. 1

• This conversion ratio is derived from guideline recommendations that establish 50mg Vyvanse as equivalent to 20mg Adderall 1
• Applying this ratio: 40mg Vyvanse ÷ 2.5 = 16mg Adderall IR

Pharmacokinetic Rationale for Conversion

The conversion accounts for fundamental differences in drug delivery mechanisms:

• Lisdexamfetamine (Vyvanse) is a prodrug that requires enzymatic hydrolysis in red blood cells to release active d-amphetamine 2, 3
• This prodrug mechanism results in a lower peak plasma concentration (Cmax) and delayed time to peak (Tmax) compared to immediate-release d-amphetamine 3
• Vyvanse produces 50% lower Cmax but identical total drug exposure (AUC) compared to equivalent doses of IR d-amphetamine 4

Practical Dosing Considerations

Start with 15-20mg Adderall IR divided into 2 doses (e.g., 10mg morning, 5-10mg midday) when converting from 40mg Vyvanse:

• Vyvanse provides therapeutic action extending 13-14 hours post-dose 3, while Adderall IR typically lasts 4-6 hours
• Multiple daily doses of Adderall IR are required to replicate the extended coverage of once-daily Vyvanse 2
• The usual starting dose for Adderall is 10mg once daily, with titration by 5mg weekly up to 50mg maximum 1

Important Caveats

Titrate based on clinical response rather than strict mathematical conversion:

• The prodrug delivery system of Vyvanse produces less pronounced behavioral activation and lower "drug liking" scores than IR d-amphetamine at equivalent exposures 4, 3
• Patients may experience different subjective effects with IR formulations due to the rapid onset and higher peak concentrations 5
• Monitor for both inadequate symptom control and stimulant side effects (insomnia, decreased appetite, cardiovascular effects) during the transition 6