It never struck me that Linda might have dabbled in that stuff--maybe it's the angelic face. So I guess it wasn't too surprising that she did as told in her first cover story for Rolling Stone:

"On the road to Bakersfield, Ronstadt talked some more about drugs. She has taken just about every drug around, she said in answer to a question. But she's given up almost every one. Grass once made her hands swell, she said. Cocaine made her "feel terrible. And I also can't take opiates." Nor can she drink. A steady diet of gin, she said, made her dizzy and she thought she had vertigo. Other drinks gave her skin rashes. She tried heroin "once or twice, but it's not for me." She can take speed and declared Methedrine her only remaining vice. "But it makes me sneeze too much."

from a posting somewhere.