If opioids are prescribed and overtaken, then your risk of becoming dependent on the drug goes up. Opioids are highly addictive.

It is interesting to note that they report potentiation of 10mg but not 5mg of morphine. Thus, it is possible that antihistamine potentiation is dependent on dose of opioid, or that antihistamines raise the analgesic ceiling. That is to say, antihistamines may raise the maximum possible effect from opioids without raising the effects of lower doses much. However, antihistamine combination did tend to enhance the effects of lower dose morphine, but the effect was not as dramatic (therefore not reaching statistical significance in a study of this power).