Internet sellers of illicit substances and so-called "legal highs" are undercutting street drug dealers by mailing their wares direct to homes, circumventing drug controls.

Australian Customs and Border protection is battling to stay abreast of the online trade and said Australian customers - which included children - may be unwittingly breaking the law as drugs marketed by online pharmacies as "legal highs" contain ingredients that are illegal to import into Australia.

Examples of some of the "legal highs" sold online. Credit:Craig Sillitoe

The drugs, sold as substitutes to more common illegal substances such as ecstasy and marijuana, are sold under names including Giggle, Diablo, Hardcore, Spice and e-Blast, "plus many others", Customs said.

Customs said some were simply caffeine-based while others had controlled ingredients such as ephedrine, one of the precursors of methamphetamine. They are sent through the post and Customs said "many packages are opened and assessed each day", but it cannot screen them all.