We show that the pre-FOMC announcement drift in equity returns occurs mostly in periods of high market uncertainty. Specifically, this abnormal return is explained by a significant reduction in the risk premium (implied volatility and variance risk premium) prior to the announcement, but only when the risk premium is high, e.g., when it is above its median. The relevant measures of market uncertainty are persistent and are not related to policy uncertainty or expectations. Markets do not become stressed in the days prior to the announcement, and the resolution of uncertainty is not reversed in the days after the meeting. Moreover, we explain why recent studies suggest that the pre-FOMC drift might have disappeared in the past decade, as this decline in the effect is due to time variation that was also present in older data. Additionally, CAPM only works on FOMC dates when the risk premium is high, e.g., implied volatility above its prior median level. The results are robust to different samples and to alternative risk premium and uncertainty measures.