To find the value of \( 8x \) given that \( 2x = -4 \), we first need to solve for \( x \).
Starting with the equation:
\[ 2x = -4 \]
We can divide both sides by 2:
\[ x = -2 \]
Now that we have the value of \( x \), we can find \( 8x \):
\[ 8x = 8 \cdot (-2) = -16 \]
Thus, the value of \( 8x \) is \( \boxed{-16} \).