According to researches, people who have been using drugs for longer period, either for some medical purpose or something else, are vulnerable to anxiety attacks. The major reason is sudden stop of drugs intake.
Anxiety attacks may also be the result of the use of recreational drugs, such as amphetamines, ecstasy, LSD, or cannabis etc. In fact, it’s also said that excessive intake of coffee can make one person more anxious than others who are not used to drinking coffee.
In a nutshell, use of drugs in general, and their unavailability causes anxiety, so avoid using them in excess.