What is the appropriate conversion dose and monitoring when switching an adult patient with attention‑deficit/hyperactivity disorder who has tolerated Adderall (mixed amphetamine salts) to Vyvanse (lisdexamfetamine)?

Adderall to Vyvanse Conversion in Adults with ADHD

When switching an adult patient from Adderall to Vyvanse (lisdexamfetamine), start Vyvanse at 30 mg once daily in the morning if the patient was taking Adderall XR 10–20 mg, or start at 50 mg if the patient was taking Adderall XR 30–40 mg, then titrate by 10–20 mg weekly based on clinical response up to a maximum of 70 mg daily. 1

Pharmacologic Rationale for Conversion

• Lisdexamfetamine is a prodrug that remains pharmacologically inactive until red blood cells enzymatically cleave the l-lysine amino acid, gradually releasing active d-amphetamine through rate-limited hydrolysis. 1, 2
• This prodrug mechanism provides a longer duration of action—up to 14 hours post-dose—and reduces abuse potential compared to immediate-release amphetamines because it avoids rapid plasma concentration spikes. 3, 2
• There is no established direct milligram-to-milligram dose equivalency between mixed amphetamine salts (Adderall) and lisdexamfetamine; conversion must be guided by clinical titration rather than mathematical calculation. 1, 4

Practical Conversion Algorithm

Starting Dose Selection

• For patients on Adderall XR 10–20 mg daily: initiate Vyvanse 30 mg once daily in the morning. 1
• For patients on Adderall XR 30–40 mg daily: initiate Vyvanse 50 mg once daily in the morning. 1
• For patients on immediate-release Adderall: sum the total daily dose and use the ranges above to select the starting Vyvanse dose. 1

Titration Protocol

• Increase Vyvanse by 10–20 mg weekly based on ADHD symptom response and tolerability, up to a maximum of 70 mg daily. 5, 1
• Therapeutic effects appear within hours of the first dose, allowing rapid assessment of efficacy. 4
• Approximately 70–80% of adults with ADHD respond to amphetamine-based stimulants when properly titrated. 5, 6

Monitoring During Conversion

• Cardiovascular parameters: measure blood pressure and pulse at baseline and at each dose adjustment, as both medications can modestly increase these parameters. 5, 1
• Breakthrough symptoms: assess for late-afternoon or evening symptom return, as Vyvanse provides extended coverage (up to 14 hours) compared to Adderall XR (10–12 hours). 1, 3
• Common adverse effects: monitor for decreased appetite, insomnia, headache, dry mouth, and irritability—all consistent with long-acting stimulant use. 5, 3, 7
• Weight and sleep: track appetite changes and sleep quality at each visit. 5, 1

Key Clinical Considerations

When to Switch Stimulant Classes

• If a patient fails to respond adequately to one stimulant family (methylphenidate vs. amphetamine), trial the alternative class before considering non-stimulants, as approximately 40% of patients respond to only one class. 5, 8
• In medication-naïve adults, 41% require a switch from the initially prescribed stimulant family within 90 days due to poor tolerability. 8

Advantages of Vyvanse Over Adderall

• Once-daily dosing improves medication adherence compared to multiple daily doses of immediate-release Adderall. 5
• Reduced abuse potential due to the prodrug mechanism, making Vyvanse preferable in patients with substance-use concerns. 5, 2
• Smoother pharmacokinetic profile with less pronounced peaks and troughs, potentially reducing side effects. 2

Common Pitfalls to Avoid

• Do not assume dose equivalency: a patient stable on Adderall 30 mg may require Vyvanse 50–70 mg for equivalent symptom control; titrate based on clinical response, not mathematical conversion. 1
• Do not discontinue Adderall abruptly with concern: no washout period is required when switching between stimulants; stop Adderall and start Vyvanse the next day. 4
• Do not undertitrate: the maximum Vyvanse dose is 70 mg daily, and many patients require this dose for optimal symptom control. 5, 1
• Monitor for late-day symptom return: if breakthrough symptoms occur in the evening, consider adding a small afternoon dose of immediate-release amphetamine (5–10 mg) rather than increasing the morning Vyvanse dose beyond 70 mg. 5

Safety and Contraindications

• Both Adderall and Vyvanse are contraindicated in patients with symptomatic cardiovascular disease, uncontrolled hypertension, hyperthyroidism, glaucoma, or concurrent MAO inhibitor use (within 14 days). 5
• Exercise caution in patients with a history of substance-use disorder; Vyvanse's prodrug design offers lower abuse potential but does not eliminate it entirely. 5, 2
• Screen for suicidality at baseline and during titration, particularly if comorbid depression or anxiety is present. 5