def get_most_popular_drugs(nonzero_df):
    """
    Get the top 3 drugs that are used by patients.
    
    Input
    -----
    df: pandas.DataFrame
        The dataframe containing patients with positive response to treatments

    Returns
    -------
    popular_df: pandas.DataFrame
        The dataframe containing the top 3 most popular effective drugs.
        This dataframe should be dimenion (3 x #).
    
    """
    drug_counts = nonzero_df.groupby(["Drug"]).count()
    popular_df = drug_counts.sort_values(by="Effect", ascending=False)[0:3]
    return popular_df