How can adderall (dextroamphetamine and racemic amphetamine) and nyquil work together?

No problem.: Presuming that you are using both meds appropriately & in doses that are effective for you, there is no problem with taking your usual prescribed Adderall (dextroamphetamine and racemic amphetamine) in daytime + short-term night-time use of nyquil. There are better meds (in both categories) but if these are effective for you, then the combo is not worrisome. Note: i would not use nyquil as a sleep med, but rather for night cough/cold.