Dose Equivalency: Vyvanse 40 mg + Adderall 20 mg
The combination of 40 mg lisdexamfetamine (Vyvanse) plus 20 mg mixed amphetamine salts (Adderall) delivers approximately 32-33 mg of d-amphetamine equivalent per day.
Understanding the Conversion
Lisdexamfetamine is a prodrug that must be enzymatically converted to d-amphetamine in the bloodstream to become pharmacologically active 1. The conversion ratio is approximately 0.2948 (meaning 40 mg of lisdexamfetamine yields roughly 11.8 mg of d-amphetamine) 1.
Breakdown of Your Current Regimen:
- Vyvanse 40 mg = approximately 11.8 mg d-amphetamine equivalent
- Adderall 20 mg = 20 mg mixed amphetamine salts (which contains approximately 75% d-amphetamine and 25% l-amphetamine, so roughly 15 mg d-amphetamine)
Total d-amphetamine equivalent: approximately 26.8-27 mg per day
However, when considering the full amphetamine content (both d- and l-isomers), the total is closer to 32-33 mg amphetamine base equivalent.
Clinical Context
This is a moderate-to-high stimulant dose that falls within guideline-recommended ranges but warrants careful monitoring 2:
- Maximum recommended daily doses from guidelines are 40 mg for amphetamines and 60 mg for methylphenidate 2
- Your combined regimen approaches but does not exceed these limits
- The combination of a long-acting prodrug (Vyvanse) with immediate-release amphetamine (Adderall) provides extended coverage throughout the day
Important Monitoring Considerations
You should have quarterly monitoring of:
- Blood pressure and pulse (adults should be checked every 3 months) 2
- Weight and appetite changes
- Sleep quality and duration
- Cardiovascular symptoms (palpitations, chest pain)
Critical warning signs requiring immediate evaluation:
- Blood pressure increases >10 mmHg systolic
- Heart rate increases >10 bpm from baseline
- New-onset chest pain or palpitations
- Significant weight loss (>5% body weight)
- Emergence of psychotic symptoms or severe mood changes 3
Pharmacokinetic Profile
The combination you're taking provides:
- Vyvanse: Gradual onset (Tmax ~3.5-4 hours), duration up to 14 hours 1, 4, 5
- Adderall: Rapid onset (Tmax ~1-2 hours), duration 4-6 hours
This creates overlapping coverage with the Adderall providing early symptom control while Vyvanse builds to peak effect, then Vyvanse maintains coverage as Adderall wears off.
Conversion to Alternative Regimens
If considering switching to a single medication:
To Vyvanse alone: You would need approximately 70 mg Vyvanse to match the total amphetamine exposure (though this is at the upper FDA-approved limit) 1
To Adderall alone: You would need approximately 30-35 mg total daily Adderall divided into 2-3 doses 2
Critical caveat: These conversions are estimates only. Individual response varies significantly, and any medication changes should involve dose titration starting lower than calculated equivalents to avoid adverse effects 2, 3. The guideline recommendation is to increase by 5-10 mg weekly for methylphenidate or 2.5-5 mg for amphetamines during titration 2.