To determine which side effects occur the most often in a set of raw medical data, the appropriate algorithm to use would be a for loop.
A for loop can be employed to iterate through the data, count the occurrences of each side effect, and then store and compare the counts to identify the most frequent ones.
Linear search and binary search are not suitable for counting occurrences, and bubble sort is not relevant for this specific task. Therefore, the best choice from the provided options is the for loop.