Adderall and Dexedrine are both psychostimulants used in the treatment of ADHD and narcolepsy. Adderall is actually not a single substance. It is comprised of various amphetamine salts, 75% of which is dextroamphetamine (the active ingredient in Dexedrine) and 25% is levoamphetamine (the left-handed mirror image or enantiomer of amphetamine).
Hence, Adderall already contains 75% Dexedrine. Medically speaking, the difference between the two drugs is the other ingredient–levoamphetamine–that makes up the remaining 25% in Adderall.
One difference between Adderall and Dexedrine is that Adderall is associated with more prominent cardiovascular side effects. For example, some of these side effects may include peripheral vasoconsctriction, elevated heart rate, and hypertension.
This effect occurs because Adderall contains 25% levoamphetamine. Levoamphetamine is more biased toward promoting norepinephrine release than Dexedrine (dextroamphetamine). Norepinephrine activates the sympathetic nervous system or the fight-or-flight response.
This increased sympathetic activity increases heart rate, blood pressure and heart contractility, among other things. Adderall may therefore have more peripheral nervous system side effects. These added side effects are related to levoamphetamine, which affects norepinephrine. Norepinephrine regulates the heart and blood vessels, so it is more active than dopamine outside of the brain.
Adderall contains levoamphetamine in addition to dextroamphetamine. Note that levoamphetamine is asslo referred to as l-amphetamine, and dextroamphetamine is d-amphetamine.
The levoamphetamine/dextroamphetamine mixture in Adderall may be more effective for certain types of ADHD. One study reported that levoamphetamine co-administered with dexoamphetamine markedly enhanced dopamine release, compared to dextroamphetamine alone.
The two isomers are probably synergistic. Levoamphetamine tends to help with sustained attention, whereas dextroamphetamine increases task reward. ADHD is sometimes called a “reward deficiency syndrome” in the medical literature. This is because individuals with ADHD don’t find mundane tasks–like doing your homework–as stimulating and rewarding.
Some inattentive symptoms of ADHD may respond better to the the levo/dextro mixture in Adderall, because of the added dextroamphetamine.
The sympathetic nervous system is colloquially referred to as the “fight-or-flight response.” Increased activation of the sympathetic nervous system helps maintain focus in life-threatening situations. One such example is being attacked by a wild animal. It could be potentially lethal to get distracted in that situation! The levoamphetamine in Adderall mimics this effect by biasing things toward norepinephrine.
Finally, on a milligram-per-milligram basis, Dexedrine (dextroamphetamine) is more potent than. This is because Dexedrine (dextroamphetamine) affects has higher binding affinities to its targets in the brain. The difference in potency of levoamphetamine and dextroamphetamine is a subject of debate.
In vitro studies indicated that levoamphetamine was 1/3 as potent. Other studies in human volunteers suggested that levo is one half as potent as dextro. Because Adderall contains both levo and dextro, dextroamphetamine is considered more potent overall.