Some of the meds coming in pill form contain lactose filler. If you are lactose intolerant then you may experience side effects from the lactose which you might mistake for side effects of the DAAs. Typically that would be some kind of intestinal discomfort but each person is different.

If your meds are being supplied by your normal source of meds, eg. the NHS, PBS, US Insurance, then I don’t know what you are supposed to do about this. It’s not like there is the choice of asking for a non-lactose version (or might there be?). For people who are paying for their own generics then their friendly compounding chemist would no doubt be able to forego the lactose on request.

While I am at it, some brand name Harvoni contains E110 which is a yellow dye. This dye can make your urine look darker than it already is. I looked it up and below are a list of side effects.
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http://www.ukfoodguide.net/e110.htm

“Side effects are urticaria (hives), rhinitis (runny nose), nasal congestion, allergies, hyperactivity, kidney tumors, chromosomal damage, abdominal pain, nausea and vomiting, indigestion, distaste for food; increased incidence of tumors in animals.
It appears to cause allergic and/or intolerance reactions, particularly amongst those with an aspirin intolerance.
Not recommended for consumption by children.
The Hyperactive Childrens Support Group belive that a link exists between this additive and hyperactive behavioural disorders in children.
Whilst being a commonly used colour in the UK its use is banned in Norway and Finland.”