[ryenamanda]

round white one side M other side 4 no box around the M

[zfennel]

http://www.drugs.com/imprints/m-4-489.html


***If that is what your pill looks like,then its Dilaudid(Hydromorphone),But this pill is an offwhite almost yellow looking color though and you said yours is white...?do some more checking around but this is what i found...and you know that this is a controlled substance right...?Its is a schedule II in the U.S.of.A so it better be prescribed to you or its illegal to posses.
Hope this helps,Have A Great Night!!