A protective barrier of thorns protects you. for 1 minute, you have a +2 bonus to AC, including against the triggering attack, and you take no damage from Magic Missile.

Additionally, when you are hit with a melee attack, the attacker must make a constitution save or take 1d6 magical piercing damage.

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, the magical piercing damage increases by 1d6 for each slot level above 2nd.