"Muggle" may mean an ordinary person to JK Rowling, but I remember when it was one of the many synonyms for marihuana.
"HUUMESANASTOA (PDF)
... marihuana hay = marihuana joint = marihuanasavuke kif = marihuana mari = marihuana maris = marihuana mary jane = marihuana muggles = marihuana pat = marihuana ... "
www.finems1.pp.fi/images/huumesanasto.pdf view as html