Assume that we have established a dose-response function for drowsiness induced by morphine and found that drowsiness occurred in 5% of people at 3 mg morphine, 20% at 6 mg morphine, 50% at 9 mg morphine, 85% at 12 mg morphine, and 100% at 15 mg morphine

Question

We then find that three alcoholic beverages induce drowsiness in 5% of people. When we give different doses of morphine to people along with three alcoholic beverages, we find that now drowsiness occurs in 20% of people at 3 mg morphine, 50% of people at 6 mg morphine, 85% at 9 mg morphine, 100% at 12 mg morphine, and 100% at 15 mg morphine. What phenomenon are we most likely observing? Explain your answer.
What will be an ideal response?

Answer 1

Most likely this is "addition" because the 3 alcoholic beverages were able to induce drowsiness alone—an effect comparable to 3 mg of morphine alone—and when combined with morphine the dose-response function for morphine shifted to the left and was parallel to the dose-response function established for morphine alone.