This study investigated the causal interactions between macroprudential policy, measured by the Macroprudential Policy Index (MPI), and financial cycles represented by the Aggregate Financial Cycle (AFC) and the Credit and Asset Prices Financial Cycle (CAFC) in South Africa from 1970q1 to 2023q2. Additionally, the study explored the effects of macroprudential policy during different phases of financial cycles. Using the time-varying Granger-causality model, the study found that the MPI Granger-caused financial cycles during the 2003/07 credit boom in South Africa, while the AFC and CAFC Granger-caused macroprudential policy during the Covid-19-induced collapse of financial markets. The results suggest that macroprudential policy is employed more proactively during financial booms and more reactively during financial busts in South Africa. The Markov switching dynamic regression model used to assess the MPI's effects revealed that macroprudential policy's effectiveness is stronger during financial busts and weaker during financial booms in South Africa. This is because financial institutions in South Africa tend to resist stricter regulations during boom phases due to heightened optimism about future prospects. Conversely, they are more receptive to stimulatory interventions during bust phases. Based on these findings, it is recommended that the South African Reserve Bank and the Prudential Authority use macroprudential policy more assertively during financial booms to enhance its effectiveness. This could involve setting more stringent parameters upon activating macroprudential policy tools or complementing macroprudential policy with monetary policy during financial booms.