Green’s Dictionary of Slang

E n.

also E-ball
[abbr. ecstasy n.]

the popular nickname of the hallucinogenic drug MDMA (methylene dioxymethamphetamine).

[UK]J. Morton Lowspeak.
[US]Eble Campus Sl. Apr. 4: E-ball – the synthetic drug Ecstasy.
[Ire]J. O’Connor Secret World of the Irish Male (1995) 58: ‘You want an E?’ [...] ‘An ecstasy?’ he explained.
[UK]R. Rendell Keys to the Street 129: A couple of Es?
[UK]Guardian G2 12 Jan. 11: Wow, just had a great spliff/line/E.
[US]Teen Lingo: The Source for Youth Ministry [Internet] ‘E’ n. Term used for the drug ‘Ecstasy.’ Sometimes called ‘X’. ‘Lets go score some “E”.’.
[Aus]L. Redhead Rubdown [ebook] Tammy ever tell you about her life when she was all googly on E?
[Aus] L. Redhead ‘Grassed’ in Crime Factory: Hard Labour [ebook] The couple of times he’d taken E he felt sloppy and out of control, telling Sharni he loved her over and over.

In derivatives