Wiktionary
high as a kite
a. (context simile colloquial English) Very much under the influence of drugs, extremely high.
Usage examples of "high as a kite".
Sassine went nervously for his gun but I didn't take any notice because he was as high as a kite and his reactions were notably slow: I could 'have got his gun and shot Zade or Ventura or possibly both as they came back from the flight deck but Kuznetski and Ramirez were behind me now and so was Shadia.
Nessie lumbers on, oblivious, her red-rimmed eyes indicating to anyone knowledgeable about these creatures that she's high as a kite on a double dose of reptile tranquilizer.