Allison Janney has been told not to "express" her "theories" about why 'Mom' was cancelled

Speaking on 'CBS Sunday Morning', she said: “It was a shock [about the cancellation]. I have my own theories, but I’ve been told not to express them. But listen, eight years is a great long run for a show.”

The comedy series has been applauded for shining a spotlight on addiction issues and Allison thinks it's important to showcase the subject on TV.

She said: “You know, it’s one thing to be part of a show that entertains, which in and of itself is a wonderful thing. But to also have an impact on people who are in recovery, or people who have loved ones or family members who are going through it, to make recovery a more approachable option.”

The 'I, Tonya' star admitted she's anxious about what's next for her now the show is ending.

She said: “I hate change. It makes me … I get afraid – I always have – to let something go and not know what’s next. I think the biggest thing I need to learn how to say is no.”

Despite her reluctance to speak on the subject, Allison previously claimed there were many reasons why the show had been cancelled and "most of them" were "probably money" related.

She also admitted news of the programme being dropped was unexpected.

She said: “I wish that we’d had at least another year for the writers to have that much time to ramp up to the ending. We sort of found out sooner than we thought we would.

“We thought, ‘Surely, they’re gonna want more 'Mom'.’ And they decided not.”