Harvoni is a combination of the antivirals ledipasvir and sofosbuvir, It works via nucleoside (and other) mechanisms to intercalate into new HCV making them inactive (and hence they cannot reproduce). In the post-release documentation from the manufacturer the elimination kinetics for the two drugs are mostly known and are not apparently effected much by hepatic metabolism: “Clinically significant drug interactions with Harvoni mediated by CYP or UGT1A1 enzymes are not expected”.
So that eliminates a lot of “worry” where substrate nutrient/herbs go (curcumin, glycyrhizin etc). Only one mentioned is St. Johns Wort via P-gp drug transport induction. There is a yet “unknown” slow oxidative metabolic step for one part (ledipasvir) which has unknown effect on the drug. All this said (and since nothing really in Phase 1 or 2 is a huge risk); The nucleoside MOA and related MOA are unlikely altered by any nutrients. The metabolism is unlikely affected by any known substrate or pathway augment in the natural realm (aside from Hypericum).
In other antiviral drug co-treatment the most commonly helpful strategy for natural meds is to support “what the antiviral does NOT do” (I simply tell patients “the antivirals are like ‘viral birth control’ they stop replication but do not help the underlying immune system nor the original virus population to eliminate, so we need to support all that”.) I use global immune support (nutrients, GSH, (NAC if you like) etc as well as cytokine manipulators (H2O2, O3, UVBI …) and broad based post-translational immunomodulators (CUrcumin, Silibinin, Artesunate, Glycyrrhizin…) and oral supports such as mushrooms, thymus extract, many herbs etc. – all as clinically indicated to cover what the antivirals “do not do”.