Rationale: Fentanyl remains the primary cause of fatal overdoses, and its co-use with methamphetamine (METH) is a growing concern. The optical isomers of METH, dextromethamphetamine (d-METH) and levomethamphetamine (l-METH), differ substantially in dose expression and thus may differentially contribute to the racemate’s bidirectional effects. Furthermore, it is unknown which of METH’s monoamine (MA) receptor mechanisms mediate these respiratory effects. Thus, systematic evaluation of monoamine receptor selective agents may identify treatment targets for OIRD. Methods: The two optical isomers of METH, d-METH and l-METH, were tested in adult male mice to determine their effects on basal and fentanyl-depressed minute volume (MVb; i.e., respiratory frequency x tidal volum) using whole-body plethysmography. Next, six selective agonists at MA receptors involved in METH’s activity [phenylephrine (PNE; α1), clonidine (CLON; α2), SKF-82958 (SKF; D1), quinpirole (QPR; D2), 8-OH-DPAT (8-OH; 5HT1A), and DOI (5HT2)] were singly tested on basal MVb, and then in combination with fentanyl. Results: d-METH elevated MVb and l-METH decreased MVb. Under fentanyl-depressed conditions, the bidirectional effects of racemic METH were recreated by d-METH while l-METH significantly exacerbated OIRD at 1.0 and 3.0 mg/kg. MVb was dose-dependently increased by PNE and SKF and decreased by CLON and QPR. Neither 8-OH nor DOI altered basal MVb. Under fentanyl-depressed conditions, SKF transiently elevated MVb, while PNE more persistently increased it, while DOI transiently increased MVb, and 8-OH decreased MVb. Conclusions: d-METH and l-METH differentially contribute to the bidirectional respiratory modulation observed with the racemate and selective activation of MA receptors altered basal respiration and OIRD.