How long do you need to have stopped marijuana before surgery?

It is critical that patients quit smoking all substances before surgery, including marijuana; these substances can have the same detrimental effects on surgery as nicotine. For example, they can make patients more or less susceptible to anesthetics. The carbon monoxide found in any kind of smoke affects blood pressure, making it more difficult for the blood to carry oxygen.

Patients should feel comfortable telling their anesthesiologist if they have been smoking or using other substances before surgery, as this information will remain confidential and is important to their care.

Source: http://www.lifelinetomodernmedicine.com/ArticlePage.aspx?ID=0f8af670-3cfb-47c3-b9f0-b54eb8f4528d&LandingID=fc6eb1da-98e4-43c7-bb9f-09c17e2a005d