Yes, laxatives can definitely alter the strength of any prescription medications you take. Are you taking these every day? If so, you need to talk to your doctor. I was anorexic/bulimic for 4 years and was addicted to laxatives the entire time and could not go to the bathroom without taking them. When I got help for my problem, my doctor was very helpful and put me on a prescription laxative which regulated my digestion and helped a lot! Over the counter laxatives are not meant to be taken on a regular basis, and it can do a lot of harm to your body, trust me, I have been through it. I believe that the prescription laxative I was on did not have any interference with medications because when I was first in recovery I had to be on a lot of them because I was very sick...and they all still worked. Over-the-counter laxatives do interfere, however. If you have chronic constipation...talk to your doc ASAP!!!!