Cannabis, as a general rule, is not a harmful or dangerous substance. The "danger" as it were, in Cannabis lies in the potential for anxiety, depression, psychological dependence and so on. There aren't any legitimate instances of humans dying or otherwise being injured by using Cannabis, save for the obvious issues i.e. inhalation of smoke etc. You don't have anything to worry about so long as you keep your Opioids dosed at a reasonable level.
You're aware that Tramadol (Ultram) is not to be taken in dosages higher than 300mg - 400mg maximum, yea? It has major potential for provoking seizures at high dosages, so it's good to know.