I have been on Topamax on and off for about 4 years, so that would have made it 2002 when I started the Rx. I went from 100mg twice a day from my Primary Care Doctor to 200mg twice a day by my pain doctor about a year ago. I have been on pain meds since 2001 and have not noticed an issue with them being less effective while on Topamax. I started on Percocet and took a dose all the way up to 10/325mg tablets. Then I was given Dauldid 4mg twice a day. Then to the Duragesic Patch 50mcg with Percocet for breakthrough pain. At which time my Topamax was doubled for nerve pain. Then to Duragesic with Dauldid. Then Duragesic was changed to 75mcg and Oxycodone (pure) for breakthrough. And now back to the Dauldid for breakthrough pain. I have not noticed the Topamax has effected my relief. Maybe it has something to do with the dose you are on before there are any effects. The only side effect I have is that soft drinks taste like dirt. I wish the best of luck!