Adderall 55mg to Vyvanse Conversion
For a patient taking Adderall 55mg daily, start Vyvanse at 70mg once daily in the morning, as this represents the maximum FDA-approved dose and accounts for the fact that lisdexamfetamine is a prodrug requiring conversion to active d-amphetamine. 1, 2
Conversion Rationale
There is no established direct dose equivalency between Adderall (mixed amphetamine salts) and Vyvanse (lisdexamfetamine), as they have different pharmacokinetic profiles despite both being amphetamine-based medications. 3 However, the following considerations guide the conversion:
Lisdexamfetamine is a prodrug that must be enzymatically hydrolyzed in the gastrointestinal tract to release active d-amphetamine, resulting in rate-limited absorption and lower peak plasma concentrations compared to immediate-release formulations. 2, 4, 5
The maximum FDA-approved dose of Vyvanse is 70mg daily for adults with ADHD, which should be the target when converting from high-dose Adderall (55mg exceeds the typical maximum of 40-50mg). 6, 1, 2
Vyvanse provides approximately 12 hours of therapeutic effect through its prodrug mechanism, offering once-daily dosing comparable to extended-release amphetamine formulations. 7
Implementation Algorithm
Step 1: Discontinue Adderall abruptly without tapering, as no washout period is required between stimulant medications. 3
Step 2: Start Vyvanse 70mg once daily in the morning on the day following the last Adderall dose. 1, 2
Step 3: Assess response within the first week using standardized ADHD rating scales, as therapeutic effects occur within hours of the first dose. 1, 3, 2
Step 4: If inadequate response at 70mg, consider that the patient may be at the ceiling of amphetamine-based therapy and evaluate alternative approaches rather than combining medications. 6
Critical Safety Considerations
The current Adderall dose of 55mg already exceeds guideline-recommended maximums (40-50mg total daily dose for amphetamines in adults), raising concerns about excessive amphetamine exposure. 6, 1
Never combine Adderall and Vyvanse, as the American Academy of Child and Adolescent Psychiatry specifically warns against combining amphetamine-based stimulants due to excessive total amphetamine exposure and increased cardiovascular and psychiatric adverse effects. 6
Monitor cardiovascular parameters closely (blood pressure and pulse) at baseline and after conversion, as both medications carry risks of cardiovascular adverse effects. 6, 1
Assess for overstimulation symptoms including increased distractibility, agitation, cognitive inflexibility, appetite suppression, insomnia, and mood changes, as excessive dosing can paradoxically worsen attention. 1, 2
Common Pitfalls to Avoid
Do not attempt to "bridge" with both medications or overlap therapy, as this creates dangerous cumulative amphetamine exposure. 6
Do not start at a lower Vyvanse dose (e.g., 50mg) assuming gradual titration is needed, as the patient is already tolerating high-dose amphetamine therapy and requires maximum therapeutic effect. 1, 2
Do not assume treatment failure if response is inadequate at Vyvanse 70mg—instead, consider switching to methylphenidate-based stimulants, as more than 90% of patients respond when both stimulant classes are properly tried. 1
Avoid administering Vyvanse with high-fat meals, as this significantly reduces early drug exposure and therapeutic effect. 3
Alternative Approaches if Vyvanse 70mg is Inadequate
Switch to methylphenidate-based stimulants (e.g., Concerta, Ritalin LA) rather than escalating amphetamine exposure further. 1
Add or switch to non-stimulant medications such as atomoxetine, guanfacine, or bupropion if stimulants are ineffective or poorly tolerated. 6, 1
Reevaluate the diagnosis and assess for comorbid conditions (sleep disorders, anxiety, depression) that may be contributing to perceived treatment inadequacy. 1