Sorry to hear about your father.
~90% of chemo patients develop nausea/vomiting. All chemotherapeutic drugs are emetogenic--it just depends on their potential (low, med, high). dronabinol (Marinol) is used
all the time for this. This is the synthetic version of THC.
What's the consensus on Marinol? It works, but nowhere near as good as smoking bud. Why? Easy. Cannabinoids. There are so many cannabinoids in bud.. allowing numerous interacions with, and modulation of the cannabinoid receptors throughout your body (which is a whole other topic--why do we even have these receptors...) along with the fact that smoking is the
fastest route of administration--it allows the user to quickly self-titrate.
So.. eating cannabutter is also an optional route to go (better than Marinol, not as good as smoking) for nausea.. it has the added benefit of being long-lasting and an altogether different experience, as well as less overall stigma. The downside to cannabutter is.. it takes at least an hour to effect, you never
really know how potent/strong it will be, different absorption rates depending on stomach environment etc.
My two cents... again good luck! And make sure he is compliant and eating healthy