A medium creature can use a heavy weapon with disadvantage of a large creature?

@llincollns a medium creature can use a heavy weapon with disadvantage of a large creature such a small creature uses a heavy weapon? not rules as written, but I'd allow it but would not allow character to cancel that disadvantage #wotcstaff

— (((Mike Mearls))) (@mikemearls) September 1, 2016

@llincollns if so, it would cause 4d6 damage with a great sword of a large creature? correct

— (((Mike Mearls))) (@mikemearls) September 1, 2016