I just switched from Dexedrine to Adderall (which only became available in Canada last month). I wanted to try Adderall because I thought its comedown effect might be better than Dexedrine's, since the different salts should wear off at different times, and perhaps the left-handed amp might help as well. I was taking one 15mg spansule of Dexedrine a day, with a bottle of 5mg tablets to take when I felt I needed more coverage. Since the levo isomer is far the weaker of the two, my doctor suggested 20mg, 25mg, or 30mg of Adderall XR. Adderall tablets are not available in Canada, so if I want to supplement I'll have to use Dexedrine, but Adderall XR is supposed to last longer than Dexedrine Spansules, or so my doctor told me, so I might not need it. Anyway, I picked the 25mg caps to try, and took my first one today. And, really, I think it's far less effective than Dexedrine. At first I thought it might have just been the lessened 'speediness' I was experiencing, and not lower efficacy, as I've been led to believe Adderall's mix of salts gives it that effect. But after trying to work on an essay I have to write, I really do think that it's working less effectively than a 15mg Dexedrine.

So, does anyone know the equivalency of the two drugs in raw dextroamphetamine, or by some other index? Pretending there are no acid components to the salts and looking at the amp molecules themselves, there would be 18.75mg d-amp and 6.25mg l-amp in Adderall to Dexedrine's 15mg d-amp, so Adderall should be stronger. The actual numbers are going to be off due to the weight of the other components, but the ratio should be equal--that is, if the other components of Adderall (aspartate and saccharate) aren't of especially high molecular weight compared to sulfate. But I doubt it's that big of a deal, so Adderall should be stronger. But I don't think it is. So, what gives?

Wow, long post.

I found the material data sheets from a company in the US that makes bulk amphetamines and opiates (I bet there is some security at that place!)
http://bulkpharm.mallinckrodt.com/_attachments/msds/d0841.htm
The LD50's for various amphetamines are:
Dextroamphetamine sulfate: Oral rat LD50: 32 mg/kg
Amphetamine sulfate: Oral rat LD50: 55 mg/kg.
Dextroamphetamine: Oral rat LD50: 38 mg/kg
Methylphenidate (for comparison) Oral rat LD50: 367 mg/kg

Unfortunately they don't list the LD50's for the Levo or Aspartate's or Saccharate's so you can't really calculate the potency that way. I searched for other LD50 figures but they varied somewhat (I thought these figures would be accurate given the source) and I didn't find any for the missing versions anyway.
If you find them later let me know, I'd be interested.
BTW, for those who don't know LD50 stands for Lethal Dose 50% - the amount of a drug that kills 50% of the rats being tested. It's one measure of the "strength" of a drug by weight.

Hmm... the data you've provided make the freebase of d-amp less toxic than the sulfate. Interesting.

Okay, I have the answer (if my calculations are correct), if anyone wants to know.

First, I looked on the web and found out that 10mg of Adderall contains, when the other components of the salts are removed, 6.3mg of amphetamine (there was a nice chart on some site).

Then, since that’s ‘amphetamine’ base it includes the l-amp, so we have to multiply by 0.75 to get the amount of dextroamphetamine base, which means that 10mg of Adderall contains roughly 4.73mg of d-amp.

Next, since I couldn’t find the equivalent of amphetamine base for Dexedrine, I decided to try to figure it out for myself. I looked up the molecular weights of amphetamine and sulfuric acid and found them to be 135.21 and 98.07. But there’s two amp molecules attached to the sulfate, making the total molecular weight 368.49. Taking a percentage (73.4) we find that the total dextroamphetamine in 10mg of Dexedrine is roughly 7.34mg.

So, if we’re ignoring l-amp we have 1mg Dexedrine=1.55mg Adderall (which if we round to 1:1.5 it makes conversions nice and easy).

So my 25mg Adderall is equal to roughly 16.13mg Dexedrine. So it should be just slightly stronger than the 15mg Dexedrines I was taking before, plus anything that the l-amp gives to it.

And I did all this on Adderall--instead of saying 'eh, whatever.' I think the Adderall is, in fact, working quite nicely (although I kinda miss the greater speediness of the Dexedrine, even though it’s probably better that I don’t have it). One drawback is that it's a good bit more expensive than Dexedrine, and my health plan with school only covers 80% of prescription drug costs, so I have to fork over the other 20% for this and the other drugs I'm taking.