Vyvanse 10 mg to Adderall IR Dose Equivalence
Vyvanse 10 mg is approximately equivalent to 3-4 mg of Adderall IR (mixed amphetamine salts immediate-release).
Pharmacologic Basis for Conversion
Lisdexamfetamine (Vyvanse) is a prodrug that is enzymatically converted to dextroamphetamine in the blood 1. According to the FDA label, Vyvanse 10 mg contains 5.8 mg of lisdexamfetamine base, which converts to approximately 3.9 mg of dextroamphetamine 1.
Adderall IR contains a 3:1 ratio of dextroamphetamine to levoamphetamine salts. The clinical guidelines establish that the starting dose for dextroamphetamine/amphetamine (DEX/AMP) is 2.5 mg, with titration in 2.5-5 mg increments 2.
Practical Conversion Approach
For clinical conversion:
- Vyvanse 10 mg → Start with Adderall IR 5 mg once daily (the lowest available tablet strength)
- This slightly overestimates the equivalent dose but provides a safe starting point
- Titrate down to 2.5 mg if side effects emerge
- The 2024 guideline notes Adderall XR starting dose is 10 mg daily 3, but for IR formulations, lower starting doses of 2.5-5 mg are appropriate 2
Key Pharmacokinetic Differences
The conversion is not straightforward due to fundamental differences in drug delivery:
- Vyvanse: Prodrug with rate-limited conversion producing lower peak concentrations (Cmax), delayed time to peak (Tmax ~3.5-4 hours for d-amphetamine), and duration of 13-14 hours 1, 4
- Adderall IR: Immediate release with rapid absorption, higher Cmax, shorter Tmax (~1 hour), and duration of 4-6 hours requiring 2-3 times daily dosing 2
Research demonstrates that Vyvanse produces more sustained amphetamine exposure with lower inter-individual variability (<25%) compared to equivalent doses of immediate-release amphetamine 4.
Clinical Caveats
Important considerations when switching:
- The 10 mg Vyvanse dose is below the typical therapeutic starting range (20-30 mg) 3
- Adderall IR will require multiple daily doses (typically BID or TID) to approximate Vyvanse's once-daily coverage 2
- Clinical studies used Vyvanse 50 mg compared to MAS-IR 20 mg TID (60 mg total daily) showing comparable efficacy 5, 6
- The prodrug mechanism of Vyvanse results in lower abuse liability scores compared to equivalent IR amphetamine doses 1, 7
Monitor closely for breakthrough symptoms between Adderall IR doses and adjust timing/dosing accordingly, as the shorter duration will not provide the extended coverage that Vyvanse 10 mg (even at this low dose) would provide throughout the day.