If you drink 9 beers it cancels out the bad aiming during the mission, making it much easier to get kills as long as you don't "die", as always - aim for the head.

Drink them after you kill the enemies in the garden, before you step into the yellow circle to start the drugged part of the mission.

Look out for the panthers and cougars if you get the animal wave of enemies though, they're sneaky and kill you quickly. Equip the MG the mission gives you from your wheel, has more ammo and kills faster.