I cant find this interview anywhere. I only see the far left leaning media sites reporting on it. No evidence this statement was actually made by John Ehrlichman. Do you have any?
CNN: https://www.cnn.com/2016/03/23/politics/john-ehrlichman-rich...
The Independent: https://www.independent.co.uk/news/world/americas/richard-ni...
Channel4: https://www.channel4.com/news/factcheck/factcheck-war-drugs-...
These were all in the first page of Google results with the query 'John Ehrlichman quote drug law'.
I dont trust any of these sources.
Otherwise, you're just rudely wasting people's time.
https://harpers.org/archive/2016/04/legalize-it-all/
His children dispute the claim, if that helps you, according the the CNN article. The man died in 1999 and it was reported years later.