Can I up my dosage of miralax (polyethylene glycol)?

Is dose-dependent... The more MiraLAX (polyethylene glycol) you take the faster it works. As a once over-the-counter dosed laxative you may not see results for 3-4 days, but as a multi-dosed colonoscopy preparation (when used under doctor's advice) expect laxation within hours. As with any laxative however understand its mechanism of action, its risks, & treatment goals & make sure you are not missing obstruction, dysmotility, inflammation.