Apparently the film's disjointed narrative is intended to be a reflection of Newton's extraterrestrial nature, and his perception of time being different to "ours" (it's explained more fully in the book).

I think it was probably a money-related issue rather than anything to do with drugs.

The cinematic mainstream was far more left-of-centre and experimental in the 1970s than it is nowadays because audiences weren't as spoon-fed, narrow-minded and generally d.u.m.b. as they are today.

No offence Ack, but any "huge Bowie fan for more than 30 years" who hasn't seen TMWFTE is faking it.