Constipation is caused by all of the following drugs EXCEPT :: (A) Neostigmine, (B) Atropine, (C) Morphine, (D) Fentanyl
Answer is A. Neostigmine is an inhibitor of acetylcholinesterase and thus acts like a cholinergic drug. Therefore, it can produce diarrhea (not constipation).
Atropine is an anticholinergic drug, thus can cause constipation.
Morphine and fentanyl are opioids. These can also result in constipation.