Previous research has indicated that anticipating positive effects from cannabis use may be linked with increased frequency of cannabis consumption, yet these expectancies remain poorly understood in adults with social anxiety disorder (SAD). Thus, our study aimed to investigate the expectancies of the effects of cannabis use in 26 frequently using adults with SAD (age: 27.9 ± 7.3 years; 54% female) and 26 (age: 27.4 ± 6.7 years; 50% female) without. While no between-group differences were observed, both groups reported expecting tension reduction and relaxation (F = 0.001; p = 0.974), cravings, and physical effects (F = 1.10; p = 0.300), but denied global negative effects (F = 0.11; p = 0.744). The trajectory of cannabis use perceptions (further investigated in 12/26 participants/group) also showed no between-group differences. Before the initial use, positive perceptions may have led to initial and continuous cannabis consumption, while the symptoms of cannabis use disorder may have contributed to repeated use. Our data indicate that, regardless of psychiatric history, frequent cannabis-using adults are more likely to report positive expectancies, which are often associated with increased patterns of cannabis consumption. Psychoeducational programs and openly discussing the risks of cannabis may be beneficial in preventing and/or reducing cannabis use in people with SAD.