McAdams is an environmentalist. She ran an eco-friendly lifestyle website, GreenIsSexy.org, with two of her friends for five years from 2007 to 2011. Her house is powered by Bullfrog renewable energy. She travels around Toronto by bicycle and does not own a car, but drives when in Los Angeles because it is "a harder town to cycle in". She volunteered in Biloxi, Mississippi and Louisiana in fall of 2005, as part of the clean-up effort following Hurricane Katrina. McAdams sat on a TreeHugger/Live Earth judging panel in 2007. She appealed for donations during the Canada for Haiti telethon in 2010. She was involved in Matter of Trust's "hair boom" efforts following the 2010 Gulf of Mexico oil spill. In 2011, McAdams supported Foodstock, a protest against a proposed limestone mega quarry in Melancthon, Ontario. In 2013, she filmed two promotional videos for the Food &amp; Water First Movement, aiming to preserve prime farmland and source water in Ontario, Canada. In 2014, she narrated the feature documentary "Take Me To The River", which investigates what is being done to try to save iconic rivers. In 2021, she participated in a video produced by Stand.earth calling on the government of British Columbia, Canada to stop logging the last old growth rainforests across the province.