Switching from Adderall 40 mg to Vyvanse: Recommended Dose
Start Vyvanse at 50 mg once daily in the morning when switching from Adderall 40 mg. This represents a reasonable conversion based on the pharmacokinetic properties of lisdexamfetamine as a prodrug that converts to dextroamphetamine, and the FDA-approved dosing guidance 1.
Conversion Rationale
Lisdexamfetamine (Vyvanse) is a prodrug that is enzymatically converted to dextroamphetamine in the blood 1. The conversion is not a simple 1:1 ratio with mixed amphetamine salts (Adderall) because:
- Vyvanse contains only dextroamphetamine (after conversion), while Adderall contains a 3:1 ratio of dextroamphetamine to levoamphetamine
- Approximately 30% of Vyvanse's weight is the active dextroamphetamine after the lysine is cleaved off
- A 50 mg Vyvanse dose delivers roughly 15 mg of dextroamphetamine systemically
For a patient on Adderall 40 mg daily (which contains approximately 30 mg dextroamphetamine and 10 mg levoamphetamine), starting Vyvanse at 50 mg provides a conservative but therapeutic starting point.
Dosing Algorithm
Initial conversion:
- Adderall 40 mg daily → Start Vyvanse 50 mg once daily
- Alternative conservative approach: Start at 30 mg if concerned about tolerability, then titrate up
- Assess response after 1 week
- If inadequate symptom control and good tolerability: increase by 10-20 mg weekly
- Maximum dose: 70 mg daily
- Target dose range for most adults: 50-70 mg daily
Key Clinical Considerations
Pharmacokinetic differences to anticipate:
- Vyvanse has a smoother, longer duration of action (up to 13-14 hours) compared to Adderall XR 3
- Peak effects occur approximately 4 hours post-dose versus 3-4 hours for Adderall 1
- Less pronounced "peaks and valleys" in symptom control throughout the day
Monitoring during the switch:
- Blood pressure and pulse at each visit (stimulants can elevate both) 4, 1
- ADHD symptom rating scales from patient and significant others
- Appetite, sleep, and weight changes
- Cardiovascular symptoms (chest pain, palpitations)
- Psychiatric symptoms (anxiety, agitation, mood changes) 1
Common Pitfalls to Avoid
Don't underdose: The most common error in clinical practice is using insufficient doses of stimulants 5. If starting at 50 mg doesn't provide adequate symptom control within 1-2 weeks and is well-tolerated, titrate upward rather than switching medications prematurely.
Don't assume equivalent dosing: A direct mg-to-mg conversion from Adderall to Vyvanse will result in underdosing. The 50 mg starting point accounts for the prodrug nature and different pharmacokinetics.
Monitor for treatment-emergent side effects: While both are amphetamine-based, patients may experience different side effect profiles. The most common with Vyvanse include decreased appetite, insomnia, dry mouth, and anxiety 1, 2. These are typically dose-dependent and may require dose adjustment rather than medication discontinuation.
Consider timing: Administer Vyvanse in the early morning (ideally upon awakening) to minimize insomnia risk. Unlike Adderall which may require twice-daily dosing, Vyvanse's extended duration allows once-daily administration 1.
Special Populations
Renal impairment 1:
- Severe renal impairment (GFR 15-29 mL/min): Maximum 50 mg daily
- End-stage renal disease (GFR <15 mL/min): Maximum 30 mg daily
Cardiovascular screening: Before initiating, ensure no underlying structural cardiac abnormalities, cardiomyopathy, serious arrhythmias, or coronary artery disease 1.
Evidence Quality Note
The FDA label provides clear dosing guidance for Vyvanse 1, and recent ADHD guidelines support flexible titration to optimize symptom control 2. While direct head-to-head conversion studies are limited, the pharmacokinetic data 1 and clinical trial experience 6, 7, 8 support the 50 mg starting dose for patients previously on Adderall 40 mg daily.