We can argue that it's not even the intention. If a government shoots civilians, there is little hope to overthrow them by riots alone. Things can change if police, army and riot police start to disobey order. Also when there is foreign aid to arm people.

FWIW, I believe that sanctions serve to

1- Limit the reach of a regime's activity overseas. Iran's government was supporting several militant groups in the middle-east. Sanctions also had a huge effect on the country's nuclear program.

2- Force them to negotiate. That actually worked with Iran (but Trump reversed it)