Here is what I have found;
http://neuro.psychiatryonline.org/article.aspx?articleid=1828814
44.3% have withdrawal
http://www.ncbi.nlm.nih.gov/pubmed/19337457
30% have withdrawal
http://www.ncbi.nlm.nih.gov/pubmed/15912562/
0% serious(?) withdrawal events
http://www.aafp.org/afp/2006/0801/p449.html
20% have withdrawal.
http://www.aafp.org/afp/2006/0801/p449.html
20%