What is the recommended dosing when switching from Adderall (amphetamine and dextroamphetamine) 40mg Immediate Release (IR) to Vyvanse (lisdexamfetamine)?

Switching from Adderall 40mg IR to Vyvanse

When switching from Adderall 40mg IR to Vyvanse (lisdexamfetamine), start with Vyvanse 50-70mg once daily in the morning, as lisdexamfetamine is a prodrug that converts to dextroamphetamine and requires dose adjustment based on the conversion ratio and individual response. 1

Conversion Rationale

The recommended approach is to start Vyvanse at 50mg daily and titrate to 70mg if needed, rather than using a direct mathematical conversion. This is because:

• Lisdexamfetamine 70mg (the maximum FDA-approved dose for ADHD) is considered roughly equivalent to Adderall 30-40mg in clinical effect, though direct mg-to-mg conversion is not appropriate due to different pharmacokinetic profiles 1, 2
• The FDA label specifies starting at 30mg and titrating in 10-20mg increments at weekly intervals up to a maximum of 70mg daily 1
• Since your patient is already on 40mg Adderall IR (a substantial dose), starting at 50mg Vyvanse is reasonable to avoid under-treatment, with room to increase to 70mg if symptom control is inadequate 1

Dosing Algorithm

Follow this stepwise approach:

1. Initial dose: Start Vyvanse 50mg once daily in the morning 1
2. Timing: Take in the morning with or without food; avoid afternoon doses due to insomnia risk 1
3. Titration schedule: If inadequate response after 1 week, increase to 60mg, then to 70mg (maximum dose) at weekly intervals 1
4. Duration of trial: Allow 2-4 weeks at the target dose to assess full efficacy before determining treatment success 2

Key Pharmacokinetic Differences

Lisdexamfetamine's prodrug design creates important clinical distinctions:

• Lisdexamfetamine is therapeutically inactive until converted to dextroamphetamine through first-pass metabolism, providing approximately 12 hours of symptom control with once-daily dosing 2, 3
• The rate-limited enzymatic conversion results in a smoother onset and offset compared to Adderall IR, which requires multiple daily doses 3
• Linear pharmacokinetics at therapeutic doses (30-70mg) allow for predictable dose-response relationships 2

Monitoring and Adjustment

Assess the following at each follow-up:

• Efficacy markers: ADHD symptom control throughout the full day (morning through 6 PM), using standardized rating scales if available 2
• Cardiovascular parameters: Blood pressure and heart rate at each visit, as amphetamines cause α- and β-adrenergic stimulation 4
• Common adverse effects: Decreased appetite, insomnia, headache, dry mouth, and irritability (most are mild-to-moderate intensity) 1, 5
• Weight changes: Particularly important in pediatric patients, though your question implies an adult patient 1

Critical Safety Considerations

Before initiating Vyvanse, confirm:

• No current or recent (within 14 days) MAOI use, as this is an absolute contraindication due to hypertensive crisis risk 1
• Cardiac history assessment for structural disease, arrhythmias, or family history of sudden death 1
• No known hypersensitivity to amphetamine products 1

Common Pitfalls to Avoid

Do not:

• Split or divide capsules—each dose must be taken as a single intact capsule or the entire contents mixed in liquid and consumed immediately 1
• Use direct mg-to-mg conversion from Adderall to Vyvanse, as this will result in under-dosing 1, 2
• Expect immediate equivalence—41% of patients require switching between stimulant families due to tolerability issues, so be prepared to adjust or return to methylphenidate-based products if needed 6
• Prescribe for weight loss—this is not an approved indication and carries cardiovascular risks 1

Alternative Consideration

If the patient has severe renal impairment:

• Maximum dose is 50mg daily for GFR 15-30 mL/min/1.73m² 1
• Maximum dose is 30mg daily for end-stage renal disease (GFR <15 mL/min/1.73m²) 1

Expected Timeline

Patients typically experience:

• Symptom improvement within the first week of adequate dosing 2
• Full therapeutic effect by 2-4 weeks at the target dose 2
• Duration of effect extending through early evening (up to 6 PM) based on parent/patient ratings 2