If you're taking it orally, 300mg meperidine(demerol) is equivalent to 10mg morphine i.m. , which is an appropriate dose for someone without opiate tolerance.
Repeated dosing of meperidine leads to accumulation of the toxic metabolite normeperidine, so this is not meant for long-term use.
Don't snort it, there's no info available on the bioavailability when insufflated, and it could be unexpectedly strong.
EDIT: I looked up your previous posts and in one post you told you've been prescribed citalopram (lexapro, was it?) The combination of demerol with citalopram can cause serotonin syndrome and is not recommended...