When taking control of a creature, does it gain summoning sickness?

Question

Let's say I have a creature in play that doesn't have summoning sickness anymore. My opponent then takes control of this creature (with for example Control Magic). Will this creature have summoning sickness again until next turn? Or will it not, because it was already on the battlefield?

Answer 1

Yes, a creature gets summoning sickness after taking control of it

302.6.: A creature's activated ability with the tap symbol or the untap symbol in its activation cost can't be activated unless the creature has been under its controller's control continuously since their most recent turn began. A creature can't attack unless it has been under its controller's control continuously since their most recent turn began. This rule is informally called the "summoning sickness" rule.

(emphasis mine)

Since your opponent has cast the spell this turn to take control over the creature, it hasn't been under its controller's control continuously this turn. Therefore it will have summoning sickness until its (current) controller's next turn.

Also note that there are cards which specifically mention that the creature gains haste after taking control of it, such as Act of Treason, while cards such as Control Magic don't. This implies that haste has a purpose here.