Studies to show morphine is better than placebo in treating what?

Here is a link for Study protocol for a randomised, placebo-controlled, single-blind phase II study of the efficacy of morphine for dyspnoea in patients with interstitial lung disease (JORTC-PAL 15) https://bmjopen.bmj.com/content/11/5/e043156 .

I would suggest you look into the drug approval process in the US, I think you will learn a lot.