About This Conversion Tool
The Vyvanse to Adderall conversion calculator is an educational resource designed to help estimate equivalent dosages between lisdexamfetamine (Vyvanse) and mixed amphetamine salts (Adderall IR/XR). The conversion is based on the molecular weight and pharmacokinetic properties of these medications. This tool provides a clinically relevant starting point for professionals considering a switch in medication, but it is not a substitute for professional medical judgment.
Understanding the Outputs
When you input a dose, the calculator provides the following information:
- Calculated Equivalent Dose: The precise mathematical conversion based on a standard ratio of approximately 2.4 mg of Vyvanse to 1 mg of Adderall.
- Nearest Available Strength: The tool identifies the closest commercially available dosage form to the calculated value, providing a practical starting point for prescribing.
- Formulation Notes: The output clarifies whether the equivalent dose applies to Adderall's extended-release (XR) formulation or the total daily dose for the immediate-release (IR) version.
How to Use the Calculator
Using the tool is a straightforward process:
- Select Conversion Direction: Choose whether you are converting from Vyvanse to Adderall or from Adderall to Vyvanse.
- Enter Current Dose: Select the patient's current medication dose from the dropdown list. If the exact dose is not listed, choose "Custom" and enter the specific milligram amount.
- Review Results: The calculator will instantly display the estimated equivalent dose of the target medication. No "calculate" button is needed; the results update automatically.
Dosing Overview
Vyvanse (lisdexamfetamine) is a long-acting prodrug, meaning it is inactive until converted by the body into dextroamphetamine. This results in a smooth, prolonged effect, allowing for once-daily administration. Doses range from 10 mg to 70 mg.
Adderall (mixed amphetamine salts) contains both dextroamphetamine and levoamphetamine. It is available in an immediate-release (IR) form, typically dosed 2-3 times per day, and an extended-release (XR) form, dosed once daily. Total daily doses can vary significantly based on patient needs.
Guidance for Switching Medications
Switching between stimulants requires careful clinical supervision. The calculator's estimate serves as a starting point for the new medication's dose. Following a switch, the patient must be monitored closely for therapeutic efficacy and potential side effects. The dose should be titrated (adjusted up or down) based on the individual's clinical response and tolerability. Factors like metabolism, patient-specific sensitivities, and the different pharmacokinetic profiles mean a 1:1 clinical effect is not guaranteed by the conversion.
Handling a Missed Dose
For both Vyvanse and Adderall XR, if a dose is missed, it should be taken as soon as it is remembered. However, if it is already late in the afternoon or evening, it is best to skip the missed dose and resume the normal dosing schedule the next day. A missed dose should not be taken late in the day as it can interfere with sleep. Never take two doses at once to "catch up." For Adderall IR, consult a physician or pharmacist for specific instructions based on the prescribed dosing schedule.
Safety Alerts
IMPORTANT MEDICAL DISCLAIMER
- This tool is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment.
- All medication changes must be prescribed and supervised by a qualified healthcare provider who can assess the individual patient's needs.
- The dosage equivalency provided is an estimate. Patient response can vary significantly. Clinical titration is always necessary.
- The developers of this tool are not liable for any decisions or actions taken based on the information it provides.
Frequently Asked Questions (FAQ)
Why is the conversion ratio approximately 2.4:1 for Vyvanse to Adderall?
The ratio accounts for the molecular weight of the inactive l-lysine molecule attached to the active d-amphetamine in Vyvanse. After this lysine is removed in the body, the remaining d-amphetamine is what provides the therapeutic effect. This calculation standardizes the amount of active amphetamine delivered.
Does the calculator work for both Adderall IR and Adderall XR?
Yes. The conversion is based on the total daily dose of active amphetamine. For Adderall XR, this is the once-daily dose. For Adderall IR, you should use the total dose taken throughout the day (e.g., 10 mg twice daily = 20 mg total daily dose).
What if the calculated dose falls between two available strengths?
The calculator suggests the nearest available commercial dose. A clinician will decide whether to start with the lower or higher available dose based on the patient's history, sensitivity to medication, and clinical goals.
Is this dose conversion exact?
No. It is a pharmacokinetic estimate based on molecular weights. It does not account for individual differences in absorption, metabolism, or the presence of l-amphetamine in Adderall, which can affect the overall clinical feel. Titration is always required.
Why is Vyvanse only taken once a day?
Vyvanse is a prodrug that is slowly converted into active d-amphetamine over several hours. This gradual conversion provides a long-lasting, smooth effect, making it suitable for once-daily administration.
Can I use this calculator to switch from another stimulant, like Ritalin?
No. This calculator is designed specifically for conversions between lisdexamfetamine (Vyvanse) and mixed amphetamine salts (Adderall). Conversions involving methylphenidate (Ritalin, Concerta) require different ratios and clinical considerations.
Does this calculator account for potential side effects?
No. While the dose conversion aims for equivalent efficacy, the side effect profile may differ between medications. Patients should be monitored for any new or changing side effects after a switch.
How is the "nearest dose" determined?
The tool calculates the mathematically precise equivalent dose and then compares it to the list of standard, commercially available strengths for the target drug. It selects the available strength that is numerically closest to the calculated value.
References
The information and conversion ratios used in this tool are derived from standard pharmacokinetic principles and official prescribing information. For detailed data, consult the sources below:
- Vyvanse (lisdexamfetamine dimesylate) Prescribing Information. U.S. Food and Drug Administration.
- ADDERALL® (mixed salts of a single-entity amphetamine product) Prescribing Information. U.S. Food and Drug Administration.
- ADDERALL XR® (mixed salts of a single-entity amphetamine product) Prescribing Information. U.S. Food and Drug Administration.
- Starr, J. (2012). Dose Equivalence for Stimulant Medications. Psychiatric Times.
