You already have stuff like inclisiran (for familial hypercholesterolemia) or patisiran available in the UE right at your local pharmacy.
The delivery is more or less sorted out, it isn't actually that complicated, mainly it is achieved by conjugating the siRNA with another small molecule that has a tropism for the target organ (like GalNac for liver targeting, see inclisiran) the biggest hurdle was to make the RNA stable enough (resistant to the degradation from the body nuclease enzymes mainly), which is achieved by using modified nucleotides (inclisiran uses a mix of methyl, fluoro and deoxy nucleotides iirc).
Reading the summary of product characteristics of Leqvio (the commercial name of inclisiran) is actually quite interesting, on the PK section of the document, they claim that "concentrations reached undetectable levels after 48h" but at the same time the drug achieves a ~50% reduction in LDL-C from baseline more than 180 days after a single dose.