First let's level set: the benefit of taking vitamins is that if you take them regularly, at some point in the future you will be better off than you are now (in other words there is no immediate perceived benefit - it requires an investment). Alternatively, a painkiller has immediate physiological benefits.
Assessing a service as a painkiller vs a vitamin is not totally black and white - generally I would say a service qualifies as a vitamin if there is no immediate perceived benefit to its use (ie it doesn't meaningfully save me time in aggregate, does not enable me to do something else that I can directly ascribe value to, doesn't reduce a painpoint I feel at this moment). A mental test I use is if someone goes from using my service for two months to immediately not using my service, how will their workflow change? If it doesn't change meaningfully, you are likely a vitamin. Note that I recognize that by this definition Facebook is a vitamin. Vitamins can make money.
So back to you. If your service does improve work/life or actually provide a "factor of efficiency improvement" over whatever their alternative is (e.g. Doing nothing) you may have a painkiller on your hands instead of a vitamin. The problem is you aren't the ultimate judge of what is a painkiller or a vitamin (you are operating on a hunch) until you go out there and try to sell it. The market will tell you.
So my advice is to spend as much time thinking about how you will package and sell this service as you are designing the service. Create a few marketing materials, hone the pitch and sit down face-to-face with as many people as makes sense and pitch them. In fact, I am 100% happy to genuinely consider purchasing this from you so you can try it on me. At the end of the day, the customer decides if you are adding value by voting with their time and dollars so developing a sales strategy early is important. You may discover you have a great service for a specific type of buyer profile but finding that buyer profile is too expensive. It happens.
I often remind myself of Ali-G's pitch to Donald Trump of a glove to prevent ice cream from getting on your hands (if you haven't seen it please watch - hilarious). Anyone who loves ice cream has this problem and the potential market of people who eat ice cream is huge. You could probably find someone willing to pay $1 for it but there is no way anyone can build a real business off this. Of course, you never know.