There is not an author, but it is ok because you don't necessarily need one. You will just adjust your citation to omit that. Are you doing an MLA works cited page?
Title of the article you are using from the website. Title of website. Last day updated. Date accessed. <website address>.
So:
"Marijuana Overdose." Drug Overdose (underlined). 2008. 27 April 2008. <http://www.drug-overdose.com/marijuana.htm>.