HDEP-28 or ethylnaphthidate is a stimulant drug of the piperidine and naphthylaminopropane groups, closely related to ethylphenidate, but with the benzene ring replaced by naphthalene. It is even more closely related to HDMP-28, which acts as a potent serotonin–norepinephrine–dopamine reuptake inhibitor with several times the potency of methylphenidate and a short duration of action. It has been sold as a designer drug since around 2015.

HDEP-28 was banned in the UK as a Temporary Class Drug from June 2015 following its unapproved sale as a designer drug, alongside 4-Methylmethylphenidate.