In a large pot, bring salted water to a boil. Add spaghetti and cook according to package instructions until al dente. Drain and set aside.

In a skillet over medium heat, melt 4 tablespoons of butter. Add minced garlic and red pepper flakes, sauté for about 1 minute until fragrant.

Add the shrimp to the skillet, season with salt and pepper, and cook for 2-3 minutes on each side until pink and opaque.

Reduce heat to low, add the cooked pasta to the skillet with the shrimp. Pour in the lemon juice and remaining butter, tossing to combine.

Stir in chopped parsley and adjust seasoning if necessary. Serve immediately.