It was legal at one stage but in truth I had to look it up now as to when is became illegal and found this:
"After the Second World War, mandrax emerged as another important psychoactive substance. Following the identification of its abuse potential, mandrax was removed from the legal market and classified as a prohibited dependence-producing drug in part I of the schedule of the South African narcotics law (Act 41 of 1971)."
I'm guessing from that (and without actually looking for and reading the Act that is was banned in 1971.
The conspiracy purports that it was being produced by the South African Government as a means of crowd control or a means to control the masses. It's a stretch at best.
(Mind you: don't put my mind into overdrive! Things have changed. Carfentanil and Ohmefentanyl come to mind now for crowd control so far as I'm concerned!)
Here's a video in which it (the conspiracy) is mentioned (also gives you some insights and a bit of history and shows clearly under what conditions it's made and some really fucking funny video footage of people falling over after a hit of what's called a "White Pipe" i.e. a combination of crushed Mandrax and weed) (it never gets old watching one or two of these dues falling on their face)!
If it gives you that "cannot be shown in your country" (or whatever bullshit like that) then let me know and I'll find another link and replace it here.