I researched and found that there was a study on whether or not weed would lower your immune system, and it was proven that your immune system is lowered by the effects of weed (the lowering of the immune system makes the body more susceptible to disease).
Similarly: If by "sick" you mean "nauseous," then yes, it is possible that smoking marijuana can make you feel physically ill. This is more likely for those who do not have previous exposure to the drug, or for those who are attempting to mix marijuana with other drugs, i.e. alcohol.
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