A nurse is caring for a client who has been brought into an emergency department of a large hospital. The client's family state that the client "took some kind of drugs. The client is dizzy, has recently vomited, and is experiencing paranoia, yelling, "Stay away from me! You are going to kill me!" The client alternates yelling with mumbling and gesturing. Their eyes are darting back and forth as they are talking to the wall. The nurse should suspect the client has used which of the following substances?