Scraping table contents from a webpage using vba with selenium
Good job once again!

I would eliminate one loop depth level - there is only a single table that you are interested it - iterate over its rows directly. And, I would switch to more concise CSS selectors to locate table rows and cells.

Also, I would rename post to a row and t_data to cell to correspond to what these variables represent:

For Each row In driver.FindElementsByCss("table#ctl00_body_MedicineSummaryControl_grdSummary tr")
    For Each cell In row.FindElementsByCss("td")
        y = y + 1
        Cells(x, y) = cell.Text
    Next cell

    x = x + 1
    y = 0
Next row