Police said the men, aged between 21 and 33, were believed to have taken illegal substances before falling ill in Pontefract.
They were admitted to Pinderfields Hospital in an unresponsive state in the early hours of this morning and received treatment for suspected overdoses.
All four are now conscious and two have since been discharged.
Detective Inspector Dave Watts, of Wakefield District CID, said: "We are currently conducting enquiries with our partners in the health service to establish the full circumstances surrounding these incidents.
"We want people, particularly in the Pontefract area, to be aware of the potential risks of using illegal substances following these admissions and would advise anyone who feels ill after taking any substance to seek urgent medical attention."
Anyone with information is asked to contact Wakefield District CID via 101 or call the independent charity Crimestoppers anonymously on 0800 555 111.