While cannabis alone has proven to be a safe medication when used alone, there are serious risks involved when you mix it with other medications. When it comes to Adderall, a combination of both when taken at the same time can make one extremely drowsy or lead to fatal conditions such as a stroke or heart attack because Adderall has been known to increase the heart rate, while cannabis can do the same in people who already have underlying heart conditions. Prolonged use over time can weaken the immune system.