Staff at the hospital, run by the Northumberland, Tyne and Wear NHS Foundation Trust (NTW) ordered a pizza on 10 December, but were dismayed when the phrase appeared on the delivery instructions.
The NTW said staff were "greatly distressed".
Neither the hospital or the pizza shop have been identified.
The trust, which runs sites in Northumberland, Newcastle, North Tyneside, Gateshead, South Tyneside and Sunderland, said it had written to the shop and removed the takeaway from its list of approved suppliers until the matter is resolved.
Will Green, head of communications at NTW, said: "Despite great efforts over recent years, mental ill health is still surrounded by prejudice, ignorance and fear.
"With one in four people experiencing some form of mental health issue in their lifetime, it is important that organisations such as ours support efforts to reduce stigma and challenge examples of stigma wherever we find them."
A pizza company labelled a hospital a "looney bin", leaving mental health workers "horrified and distressed".