dowels have certain limits
Dowels will not prevent the pieces from rotating which is why they are often used in pairs. This pairing acts more like a mortise and tenon to resist certain forces. The Domino or loose tenon will do the same, and is better than a single dowel.
For chair legs or tables where there may be side forces, use 2 dowels if possible when joining a vertical to a horizontal piece. Also drill the hole a bit deeper than needed to allow a place for the glue to push into OR make a groove on the dowel to allow the glue to press out of the hole ....common doweling practice.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)