Beta-dichroine a quinazolinone also called febrifugine from the leaves of hydrangeas is 64-100 times more potent than quinine as an antimalarial in animals, but extremely toxic. A synthesised tolyl derivative, methaqualone (2-methyl-3-o-tolyl-4(3H)-quinazolinone), was found to be a mild hypnotic, and marketed in the sleeping tablet, Mandrax. Widely abused and quickly banned by most countries. Illegal manufacture continues and in South Africa methaqualone is the commonest drug of abuse, mixed with cannabis and smoked.

Hydrangea blooms are sometimes smoked to induce a hallucinogenic and euphoria inducing effect, a cheaper alternative to cannabis.