The TL;DR for the article is that because of bans on medications in Australia, it's difficult to find ways to ease the pain for people dying.
Secobarbital isn't banned in the US...it's just impossible to get because it's not often prescribed in the US -- and the manufacturers have taken a political stance against lethal injection (similarly, sodium thiopental is in short supply). So even legitimate patients can't get the meds they've been prescribed.