What is the Vyvanse (lisdexamfetamine) equivalent to Adderall (amphetamine and dextroamphetamine) 20mg?

Vyvanse Equivalent to Adderall 20mg

Vyvanse 50mg is approximately equivalent to Adderall 20mg in terms of clinical effect, though the pharmacokinetic profiles differ significantly with Vyvanse having a longer duration of action and more gradual onset.

Pharmacological Comparison

Vyvanse (lisdexamfetamine) and Adderall (mixed amphetamine salts) are both stimulant medications used for ADHD treatment, but they have important differences:

• Mechanism of Action:

  • Vyvanse is a prodrug that requires enzymatic conversion in the bloodstream to release active d-amphetamine 1
  • Adderall contains a 3:1 ratio of dextroamphetamine to levoamphetamine in an immediate-release or extended-release formulation 2

• Pharmacokinetic Differences:

  • Vyvanse has approximately a 0.6-hour longer lag time before onset compared to d-amphetamine 3
  • Peak plasma concentrations occur about 1.1 hours later with Vyvanse compared to d-amphetamine 3
  • Vyvanse provides approximately 12 hours of coverage while Adderall IR requires twice-daily dosing 2

Dose Equivalence

The conversion between Vyvanse and Adderall is based on the following factors:

1. Vyvanse is approximately 0.29 times the molecular weight of d-amphetamine, meaning 100mg of lisdexamfetamine converts to approximately 29mg of d-amphetamine 3

2. Adderall 20mg (mixed amphetamine salts) provides approximately the same amount of active amphetamine as 50mg of Vyvanse after enzymatic conversion

3. The total exposure (AUC) is similar between equivalent doses, though the timing differs 3

Clinical Considerations

When switching between these medications, consider:

• Duration of Effect:

  • Vyvanse provides more consistent coverage throughout the day (12 hours) 2
  • Adderall IR requires twice-daily dosing, while Adderall XR provides coverage for approximately 8-10 hours 2, 4

• Onset of Action:

  • Vyvanse has a more gradual onset due to the need for enzymatic conversion 1
  • Adderall has a more rapid onset of action 2

• Abuse Potential:

  • Vyvanse was designed with a unique delivery system that may lower abuse risk compared to immediate-release stimulants 4
  • However, research shows similar peak subjective effects (drug liking, high) between equivalent doses of lisdexamfetamine and d-amphetamine 3

Monitoring Parameters

When using either medication, monitor:

• Appetite, weight, sleep disturbances, mood changes, and growth parameters regularly 5
• Blood pressure and heart rate, as both medications can cause cardiovascular effects 3
• Efficacy in reducing core ADHD symptoms of hyperactivity, impulsivity, and inattention 2

Common Pitfalls to Avoid

• Dosing Errors: The numerical dose values are not directly interchangeable (20mg Adderall ≠ 20mg Vyvanse)
• Timing Considerations: When switching from Adderall to Vyvanse, patients may perceive a delayed onset of action
• Expectations: Patients should be informed that while the medications are pharmacologically similar, individual responses may vary
• Administration: Unlike Adderall XR which can be sprinkled on food, Vyvanse capsules should be taken whole or dissolved completely in water 4

Practical Conversion Algorithm

1. For patients on Adderall 20mg (immediate-release or extended-release):

   • Initial conversion to Vyvanse 50mg is appropriate
   • Titrate based on clinical response after 1 week

2. For patients requiring dose adjustments:

   • Vyvanse dosing typically ranges from 30mg to 70mg daily
   • Each 10mg of Adderall roughly corresponds to 25mg of Vyvanse

Remember that individual patient factors including metabolism, comorbidities, and concurrent medications may necessitate dose adjustments beyond this general equivalence.