It would be illegal if you use those products without being an authorized distributor/reseller of those companies.
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This is, in general, not going to be a problem, but I strongly urge you to discuss with a lawyer in private so your particular facts and circumstances can be evaluated.
There are a number of pitfalls you need to be aware of if this is the business model you are endeavoring to pursue.
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It would certainly be a problem if you take the pills out of a bulk pack and individually package them. that would be reverse passing off and you might run afoul of FDA regulations.
Become an authorized distributor for the products you want to include. Chances are the manufacturer will be willing to work with you. Either selling directly or through another distributor.