Just to say that I have experienced the same issue with Elvanse (which is Lisdexamfetamine – the same as Vyvanse). I was looking around to see if this was common. It does seem to happen in some people, but not many.
I found some information that might be helpful to others finding this thread, which basically backs-up what KLEMON422 has said.
Although it does only refer to amphetamine, and methylphenidate is not amphetamine and works on a different system. I can’t find any mention of difficulty passing urine with methylphenidate, so I would be interested to know if anyone has experienced the same effects with it.
“Pharmacologic actions of amphetamines are qualitatively similar to those of ephedrine and include CNS and respiratory stimulation and sympathomimetic activity including pressor response, bronchodilation, and contraction of the urinary bladder sphincter.“
And there is this:
“Other Smooth Muscles. In general, smooth muscles respond to amphetamine as they do to other sympathomimetic amines. The contractile effect on the sphincter of the urinary bladder is particularly marked, and for this reason amphetamine has been used in treating enuresis and incontinence. Pain and difficulty in micturition occasionally occur.”
Goodman & Gilman’s
The Pharmacological Basis of THERAPEUTICS
ADRENERGIC AGONISTS AND ANTAGONISTS
Thomas C. Westfall and David P. Westfall