Snappy answers that cancer patients can use when asked 

"Why do you use marijuana for medicinal purposes?"

"I had to go to the bathroom, and marijuana was the only way that I
could remove the toilet from my face."

"I am getting bored with all the different substances I have thrown up, so I thought I'd take a short break."

"Hey, I went to the trouble to get cancer just for this purpose."

"I thought I'd try eating cookies instead of tossing them."

"I'll answer you in a minute, but let me wipe the chunks off my chin first."

"I'm trying to increase my appetite, because I thought people
might be getting jealous of my new gaunt look."

"Keep that marijuana away from me, I'm trying to break the record
for unchucking the most days in a row."

"I don't really want marijuana, I'd rather get dehydrated
so I can stay in the hospital and get another delicious IV drip."

"Don't worry, if I accidently get high from the marijuana, I will bring
myself down by reminding myself that I have cancer."

"Why would I want marijuana, when I can lie here and choke on my vomit?"

"I only smoke marijuana so I won't barf up another lung,
like I did after my last chemo."

"Gee, I thought it might be a good idea stop throwing up long enough
to keep down my anti-nausea medicine."

"I admit that having my eyes bug out after five hours of uncontrollable upchucking, sure beats taking a single hit of evil puke-inhibiting marijuana."

"I thought that cancer was the gateway disease to becoming a Dead Head."

"If I throw up one more time, I am going to have to change my name to Ralph."

"I'd love to debate the issue, but let me empty my puke bucket first."