Gas-X, which contains simethicone, typically starts working within 15 to 30 minutes to relieve gas symptoms. It works by breaking up gas bubbles in the digestive tract, making it easier to expel gas and reducing discomfort from pressure and bloating. The relief time may vary depending on the dose, form of Gas-X (chewable tablets might work faster), and when it is taken, ideally at the first sign of gas discomfort after meals or at bedtime.