Constipation is caused by all of the following drugs EXCEPT :
Neostigmine
Atropine
Morphine
Fentanyl
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.