Let's presume that you've been prescribed 20mg Adderall, but want to switch to Vyvanse. What's an equivalent dose of Vyvanse that would be comparable to 20mg of Adderall?
It turns out that comparing Vyvnase vs Adderall dosages is not straightforward, for a number of reasons. But we've made a handy chart to make converting between Adderall and Vyvanse dosages a little easier.
*adjusted for relative potency of d-amphetamine : l-amphetamine
Let's say you normally take 10mg of Adderall, twice a day. What would be the equivalent dose of Vyvanse?
You'll notice that a 20 mg total dose of Adderall corresponds to 37 mg of Vyvanse. Now, there isn't a Vyvanse capsule that contains exactly 37 mg, but your psychiatrist can be prescribe you 30 mg or 40 mg (which are available), at their discretion.
To convert from an Adderall dosage to the equivalent dose of Vyvanse, multiple your Adderall dose by 1.85
The calculation to arrive at these dose equivalences is actually fairly convoluted. The molecular weights of lisdexamfetamine dimesylate (Vyvanse) and the four amphetamine salts that comprise Adderall, as well as all the relevant counter-ions were taken into account.
The above table reveals that a 30 mg dose of lisdexamfetamine dimesylate (Vyvanse) contains roughly 8.9mg of d-amphetamine (based on the relative molecular weights of the components).
However, Adderall contains both a mixture of d-amphetamine (3/4) and l-amphetamine (1/4). L-amphetamine, it turns out, is about 1/2 as potent as d-amphetamine. Therefore a 30mg dose of Adderall containing 14.2mg of d-amp and 4.5mg of l-amp will be roughly equivalent to a 16.45mg dose of d-amp.
I suggested previously that the potency of d-amphetamine to l-amphetamine is 2:1, i.e., d-amp is twice as potent. What is this claim based on?
A study conducted in 16 healthy volunteers in 1997 reported an efficacy ratio of 2:1. However, other studies have questioned the validity of these results and so the precise difference in potency remains disputed.
The pharmacology underlying this difference in potency is complex, but is probably in part related to the observation that d-amphetamine inhibits noradrenaline (NE) reuptake almost twice as strongly, and dopamine reuptake almost five times as strongly compared with l-amphetamine. However, this is only part of the story since amphetamine is also a potent monoamine releasing agent. Amphetamine's activity as a releasing-agent is more important to its therapeutic action than as a re-uptake inhibitor.
#Vyvanse vs Adderall: Pros & Cons
|Vyvanse Pros & Cons||Adderall Pros & Cons|
|Slow release mechanism allows for longer relief from ADHD symptoms||May be more effective for some times of ADHD|
|More expensive, generics are unavailable||Less expensive, generics available|
|Less abuse potential||Greater risk of psychological dependence|
|Slow release has better tolerability||Better control of dosing (e.g., can take only one Adderall if only 6 hours of symptom relief is needed)|