Usually the prostate: BPH narrows the urethra as it grows, per NIDDK - the stream loses force, hesitates, stops and starts, and the bladder stops emptying fully - drifting in over years so gradually men adapt without noticing.
Other causes: urethral stricture (scarring - faster onset), weak bladder muscle, medications (decongestants, some antihistamines and antidepressants), prostatitis when pain rides along. Worth a visit even when mild: untreated obstruction slowly damages the bladder. Urgent: cannot pee at all - acute retention, emergency care same hour.
What to do
Common questions
Why is my urine stream weak?
In men, a weakening stream usually tells a prostate story. The mechanism per NIDDK: as BPH grows the gland around the urethra, the passage narrows - so the stream loses force, takes longer to start (hesitancy), stops and starts, and leaves the bladder not quite empty. The tempo is the tell: BPH drifts in over years, and men adapt without noticing until it is well along. Other causes exist: urethral stricture (scar tissue narrowing the pipe - often after infection or injury, tends to arrive faster), a weak bladder muscle, medications (decongestants and some antihistamines tighten the outlet; antidepressants can too), and prostatitis when pain and burning ride along. The practical response: it is worth a visit even when mild - the exam, urine test, and flow check sort the causes, BPH treatment is effective and often starts with small habit changes plus medication, and untreated obstruction slowly damages the bladder muscle (better caught before that). The urgent line: if you cannot pee at all - painful, full, nothing coming - that is acute retention: emergency care, same hour. Blood in the urine or fever with urinary symptoms: same-week visit. Pymander, a free AI doctor available 24/7 by text, can help you map the timeline.