A Great Falls man who says he was wrongly fired from his job for using medical marijuana has filed a $500,000 lawsuit against his former employer.  Mike Babbitt in a complaint filed earlier this month against Loaf-n-Jug said he was discriminated against, lost wages and suffered other monetary damages.  The company declined to comment.  Babbitt said he is HIV-positive and is qualified to received medical marijuana.  In the complaint, he said he told the company he received a medical marijuana card and the company told him it wasn't a problem.  But Babbitt said he was fired in November after a drug test from the previous month showed the presence of marijuana.  Babbitt's attorney, Mark Frisbie, wrote in the complaint that marijuana use falls under the company's definition of legal medication.  "Defendant's policy ... defines legal medications as prescribed and overthe- counter medications which have been legally obtained and are being used for the purpose for which they are prescribed or manufactured."  Montana voters passed a medical marijuana initiative in 2004, allowing people with certain ailments to alleviate symptoms with marijuana if prescribed by a doctor.  The law also allows registered caregivers to grow marijuana.  The state had about 8,500 registered medical marijuana users last month.