![Razz :P](./images/smilies/icon/razz.gif)
I would tend to say, though, that the passage about the Rossak drug implies that it created true Reverend Mothers with Other Memory. Essentially any poison narcotic that brought on a near death experience with awareness of the little "psychokinesthetic extension" mote like that Jessica used to reconfigure the WoL would do the trick. But not as well as the spice essence/WoL.
(Edit: I'm not really happy with some of that. There's a bit of inconsistency in the originals IMHO, starting with FH's use of "spice essence", etc. If the earlier BG could use other narcotic poisons to create RMs and open up Other Memory, why couldn't the later ones have done the same when the spice became scarce? [To create new RMs from acolytes, I mean. Any RM who had used spice to become one was addicted to it, of course, and had to have it.] Maybe using the spice had some effect on subsequent generations that rendered them incapable of using the other, older alternatives?)