As much as the terminology used makes it sound like weed, I'm fairly sure Tolkien intended it to be tobacco.
He definitely did. He was a keen pipesmoker, and very definitely not a stoner. (edit: I think he even pins it to "a plant of the genus Nicotiana" or words to that effect in the LotR appendices)
Peter Jackson's presentation of it in the movies though... yeah. No ambiguity there. His hobbits were blazed 24/7.
Yes. "weed" was slang for tobacco in middle and early-modern English (shortly after it was introduced to England). This is where he got the term from.
The Appendix offers a number of additional suggestions, including this.
Turns out i've already beaten the LOTR challenge mode in a sense. Rainy saturday, all day LOTR marathon on TBS, sack a nugs, plenty of grub to eat while watching the movie all day