This is by no means a comprehensive list of systemic medications that cause gingival (gum) overgrowth, but it's a base reference:
Calcium Channel Blockers (Dilitiazem, Felodipine, Nifedipine, Nisoldipine, Verapamil)
Immunosuppressive Agents (Cyclosporin A, Mycophenelate Mofetil)
DeRossi S and Hersh E, A Review of Adverse Oral Reactions to Systemic Medications, General Dentistry, March-April 2006, Vol 54, No. 2, pg 131-138.
Hans Skariah, B.Sc., DMD
Promenade Court Dental Health Group in Mississauga
2233 Hurontario St., Mississauga, ON, Canada
(1/2 km north of the QEW in the Dome Building)