I hate to say this because mixing these with anything, let alone by themselves, is never a good move... but pharmacologically it makes sense.
Barbiturates.
I have a prescription for seconal and 30mg IR adderall. 30mg's is the only dose that works for my ADHD, but the problem with taking it is when I take it for classes after 6pm it severely cuts into my sleep. The effects of amp may very well not be noticable after 4 hours, but it definitely keeps me awake for at least 6 - 7 hours after I've eaten it. I also get into trouble when I take a dose of adderall or dexedrine at night and find my work done after 1 - 1.5 hours, because it means I'll be awake for 6 hours more when it isn't necessary. I've got a prescription for 2mg xanax, but honestly it's just a waste of xanax to try to kill off the effects of 30mg's of amphetamine 1 - 2 hours in. This brings me to barbs..
Barbiturates have a unique mechanism of action, and do more than benzo's do not just by being "stronger". This is because barbs, unlike benzos, also inhibit AMPA, as well as induce the CYP family of enzymes. This is important for three reasons.
1. Increasing the effects of gaba will obviously help to "slow down" the body, though sometimes not enough to produce sleep, or the ability to sleep.
2. Inhibiting the AMPA receptor. AMPA is the main excitory receptor, and though DA, NE, and SE are responsible for amphetamines actions, down the line the successful transmission of these neurotransmitters is facilitated by AMPA. You can think of AMPA as the opposite of GABA. By blocking the AMPA receptor, barbiturates decrease the ability of DA, NE and SE cells (or any cells for that matter) to respond to, and release pre-synaptically, subsequent DA, NE and SE when stimulated by post-synaptic activation of DA, NA, and SE receptors. Thus, signal transduction fails. To put it in simpler terms, barbiturates make the cells less able to continue neurotransmitter facilitated release of the same neurotransmitters downstream because they make the cell "unable" to send the signal to release more of that neurotransmitter. I hope this makes sense.
3. Barbiturates induce the enzyme family responsible for breaking down amphetamine... the CYP450 family. By inducing the CYP450 family, you're speeding up the metabolism and elimination of active amphetamine from your body.
Taking these 3 things into account, it is no surprise that pharmacologically barbiturates are by far the most superior way of "killing" an amphetamine dose (next to antipsychotics, of course). But as I said above, I hesitate to tell people this because of the sheer danger of barbiturates... however in the interest of neurochemistry I felt that this post was necessary. I can also personally attest to the effectiveness of barbiturates in killing off the action of amphetamines.
In no way am I advocating the use of barbiturates in any way shape or form, except under strict doctor supervision... I just thought it would make an interesting addition to this thread.