Can 20 mg Dextroamphetamine Be Added to 70 mg Vyvanse?
No, adding 20 mg dextroamphetamine to 70 mg Vyvanse should not be done, as this combination would exceed the maximum recommended daily amphetamine dose and significantly increase cardiovascular and psychiatric risks without established safety data for such combined dosing.
Rationale Based on FDA Labeling and Guidelines
The FDA-approved maximum dose of Vyvanse is 70 mg/day 1. Since 70 mg of lisdexamfetamine converts to approximately 40.5 mg of dextroamphetamine 1, you are already at the maximum approved amphetamine exposure. Adding 20 mg immediate-release dextroamphetamine would bring the total dextroamphetamine exposure to approximately 60.5 mg/day.
Why This Matters:
Guideline-based maximum doses: Historical ADHD treatment guidelines indicate maximum daily doses of dextroamphetamine/amphetamine at 40 mg for DEX/AMP in adults, with some patients treated up to 0.9 mg/kg or approximately 65 mg only when clearly documented that lower doses failed and higher doses produce no side effects 2
The 70 mg Vyvanse already delivers maximum approved amphetamine: Lisdexamfetamine is hydrolyzed in the blood to release dextroamphetamine over time 1. The pharmacokinetics show that 70 mg Vyvanse produces steady-state dextroamphetamine levels with a Tmax around 3-4 hours and elimination half-life of 10-11 hours 1, 3
Critical Safety Concerns
Cardiovascular Risks
The FDA label explicitly warns to avoid use in patients with serious cardiac disease and mandates blood pressure and pulse monitoring 1. Exceeding maximum doses amplifies risks of:
- Hypertension and tachycardia
- Serious cardiovascular events
- Peripheral vasculopathy including Raynaud's phenomenon
Psychiatric Risks
Higher amphetamine doses increase risk of:
- New psychotic or manic symptoms 1
- Severe agitation and anxiety
- Serotonin syndrome, particularly if combined with other serotonergic agents 1
Abuse and Overdose Potential
Both medications are Schedule II controlled substances. The combination creates:
- Higher total amphetamine burden with linear dose-proportional pharmacokinetics up to 250 mg for lisdexamfetamine, indicating lack of overdose protection 4
- Immediate-release dextroamphetamine has higher abuse potential than lisdexamfetamine 5, 4
Alternative Approaches If 70 mg Vyvanse Is Insufficient
1. Optimize Timing and Formulation
- Assess whether symptom coverage gaps are due to Vyvanse wearing off (typically 10-13 hours duration)
- Consider splitting the dose or adjusting timing rather than adding another stimulant
2. Switch to Alternative Stimulant
Guidelines recommend trying a different stimulant class if inadequate response occurs 2, 6:
- Switch from lisdexamfetamine to methylphenidate-based products
- Approximately 90% of patients respond when both stimulant classes are tried 2
3. Add Non-Stimulant Augmentation
- Atomoxetine, guanfacine, or clonidine as adjunctive therapy
- These have established safety profiles for combination with stimulants 6
4. Re-evaluate the Diagnosis and Comorbidities
- Inadequate response at maximum stimulant dose warrants reassessment
- Screen for comorbid conditions (anxiety, depression, sleep disorders) that may be limiting response
- Consider whether non-pharmacological interventions are optimized
Common Pitfalls to Avoid
- Do not assume "more is better": Stimulant response does not always increase linearly with dose, and side effects increase disproportionately
- Do not combine stimulants without clear documentation: If you proceed despite recommendations, document failed trials at lower doses, absence of cardiovascular contraindications, and close monitoring plan
- Do not ignore medication adherence issues: Poor adherence may masquerade as inadequate efficacy 6
Monitoring Requirements If Higher Doses Are Considered
If clinical judgment dictates exceeding standard maximum doses (which should be rare and well-documented):
- Baseline and ongoing: ECG, blood pressure, pulse, weight
- Psychiatric screening: Family history of mania/psychosis, current mental status
- Monthly initially: Cardiovascular parameters and symptom/side effect ratings
- Document clearly: Why lower doses failed, absence of side effects at higher doses, and ongoing benefit-risk assessment 2
The evidence strongly supports staying within FDA-approved maximum doses and exploring alternative strategies before combining stimulants at supratherapeutic levels.