Sunkist being an orange drink - orange and citrus are rumoured (emphasis on rumoured) to either lessen or increase the effects of a psychedelic substance, particularly LSD.

Sudafed - not sure if y'all have it there, but over here Sudafed is an over-the-counter nasal decongestant - the actual drug is Pseudoephedrine. Sudafed is frequently used in drug labs when preparing speed. I believe the drug itself does speed up your metabolism in a similar way to speed.

Not sure if that's what's intended here, but that's how I would tied Sudafed into the drug theme.