Click on Format | Paragraph | Indents and Spacing. The default line
spacing setting is "single", which means that if you raise or lower
characters on a line, extra height is automatically added to that line.
Change the line spacing to "exactly" some amount (try 120% of the font
size as a starting point).

jsg wrote:

How do I lower specific characters (e.g., lowering semicolons by 1 or 1.5
point in Century font; otherwise, it looks strange) without affecting the
spacing between lines? Thanks.