Is it permissible to fast after taking medicine and drinking water at the time of the Fajr athan?

Fasting is not valid if a person consumes medicine and drink during the Fajr adhan, because Allah Almighty says: "And eat and drink until the white thread of dawn becomes distinct to you from the black thread [of night]."

Fasting is only valid if the muezzin gives the adhan before the true dawn appears and this is clear, as the criterion is the true dawn. However, if the muezzin gives the adhan at dawn, or if the muezzin's mistake is not clear, then fasting is not valid after hearing the adhan.