What medicine is good for excessive/involuntary passing of urine?

Depends: You are young, and did not say if you are male or female, but this mattters quite a bit for your concerns. Ditropan (oxybutynin) is a medicine that comes in short and long lasting formulations , but is typically used in neurologic diseases with bladder problems. If you may be pregnant, you must see your physician immediately.

Several: There are several medications and also non pharmacological treatments for involuntary passing of urine ( incontinence). Some medications are anticholinergics class of medications, local estrogen application, duloxetine etc. Other techniques used are timed voiding, pelvic floor muscles exercise, surgeries, small interventions.