Green’s Dictionary of Slang

moggie n.2

also mogie

(drugs) Mogadon, a mild sleeping pill; thus moggified adj.; cit. 1989 is erroneous.

[UK]J. Morton Lowspeak 99: Moggies – amphetamines.
[Scot]I. Rankin Strip Jack 62: Cath Kinnoul was on drugs, tranquillizers of some kind [...] Valium? Moggies even?
[UK]I. McDowall A Study in Death 272: After a nightcap of moggified whisky or decaf.
[UK]N. Griffiths Grits 92: Glad a dropped those mogies before, like, calm me down a bit like.
[Scot]T. Black ‘Eat Shit’ in Killing Time in Las Vegas [ebook] I took a bucket of Moggies, how else you think I sleep.

In phrases

moggie up (v.)

(N.Z. prison) to consume a Mogadon or other sleeping tablet.

[NZ]D. Looser Boobslang [U. Canterbury D.Phil. thesis] 118/1: moggie up v. to take sleeping tablets, esp. Mogadon.