There are no official guidelines to assist in answering this question. I will search for relevant research papers instead.
The FDA Drug Labels for tamsulosin (PO) do not address this question.
From the Research
Effectiveness of Flomax (Tamsulosin) for Women with Ureteral Stones
- The effectiveness of Flomax (Tamsulosin) for women with ureteral stones measuring 4 millimeters in diameter is unclear based on the available evidence.
- A systematic review and meta-analysis published in 2017 1 found that tamsulosin significantly improves stone passage in patients with larger stones (5 to 10 mm), but the effect is diminished in those with smaller stones (<4 to 5 mm).
- Another study published in 2019 2 found that tamsulosin is effective and relatively safe in patients with ureteral stones as a medical expulsive therapy to facilitate stone passage, but the benefit is significant only for stones greater than 5 mm.
- A randomized clinical trial published in 2018 3 found that tamsulosin did not significantly increase the stone passage rate compared with placebo for symptomatic urinary stones smaller than 9 mm.
- A study published in 2014 4 found that the addition of tamsulosin to conservative treatment of distal ureteral stones showed no significant difference in stone expulsion, but reduced the duration of expulsion, pain, and need for analgesic.
Stone Size and Tamsulosin Effectiveness
- The available evidence suggests that tamsulosin is more effective for larger stones (5 to 10 mm) than smaller stones (<4 to 5 mm) 1, 2.
- For stones measuring 4 millimeters in diameter, the evidence is limited, and the effectiveness of tamsulosin is unclear.