In my understanding, efficacy refers to the performance of an intervention under ideal and controlled circumstances, effectiveness refers to its performance under ‘real-world’ conditions, and efficiency is about doing things economically, whether in terms of time, energy, or money.
Efficacy and effectiveness exist on a continuum, with efficacy trials determining whether an intervention produces the expected result under ideal circumstances and effectiveness trials measuring the degree of beneficial effect under ‘real world’ clinical settings. Efficiency is about doing things in the most economical way. In clinical trials, two drugs could be equally effective, but if one of them is much more costly than the other one, that drug won’t be considered as efficient