How much lactulose can i take without overdose symptoms?

Low toxicity: Lactulose is one of the safest of all medicines. Take the dose your physician recommends, or if you are determined to experiment, until you can't stand the diarrhea any more.

I agree however: I agree with the previous answer, since most people taking lactulose stop taking it for that day, after having more than 3 bowel movements in 1 day, however electrolyte abnormalities have been reported with excessive use, especially in your sodium levels. This is very rare and usually is a result of dehydration from excessive bowel movements > 8 per day for a few days, but overall it is safe.