Many analgesics are based on the same compounds of heroin. Everything from over the counter painkillers such as codeine to morphine lolly pops for those with severe chronic pain very often are the only treatment options for those who suffer daily or are involved in trauma.
Fentanyl is used routinely in endoscopic procedures, for example. Now, it's being heavily, heavily abused (in the US mainly), as it makes the user feel so incredibly good - one could say it alters the mind both emotionally and quite literally by blocking pain receptors. It's causing a horrendous number of deaths due to its being 100x (or something like that) the strength of morphine. Ketamine is another example of a tranquilliser used in the case of dislocated limbs/severe trauma, but also used as a party drug.
I'm sure there are some brothers and sisters who feel that taking a medication containing the same compound as a recreational drug may not be acceptable to them, and that's certainly a conscience matter - especially for those who may have suffered with their own addictions. I personally think regarding this particular study that if it's controlled and used in a professional way, more than likely side-by-side with psychosocial therapies (that is to say, if it actually is proved to be an effective treatment), it may greatly benefit those who have treatment resistant depression and would be no different to using opiates to control pain. Because the aim isn't to get high, the aim is to reset the brain in the same way ECT is thought to work.