Background and Aims: Inflammatory bowel disease (IBD) patients suffer from significant morbidity and diminished life quality. The plant cannabis is beneficial in various gastrointestinal diseases, stimulating appetite and causing weight gain. Our aims were to assess whether treatment with inhaled cannabis improves quality of life, disease activity and promotes weight gain in these patients. Methods: Patients with long-standing IBD who were prescribed cannabis treatment were included. Two quality of life questionnaires and disease activity indexes were performed, and patient’s body weight was measured before cannabis initiation and after 3 months’ treatment. Results: Thirteen patients were included. After 3 months’ treatment, patients reported improvement in general health perception (p = 0.001), social functioning (p = 0.0002), ability to work (p = 0.0005), physical pain (p = 0.004) and depression (p = 0.007). A schematic scale of health perception showed an improved score from 4.1 ± 1.43 to 7 ± 1.42 (p = 0.0002). Patients had a weight gain of 4.3 ± 2 kg during treatment (range 2–8; p = 0.0002) and an average rise in BMI of 1.4 ± 0.61 (range 0.8–2.7; p = 0.002). The average Harvey-Bradshaw index was reduced from 11.36 ± 3.17 to 5.72 ± 2.68 (p = 0.001). Conclusions: Three months’ treatment with inhaled cannabis improves quality of life measurements, disease activity index, and causes weight gain and rise in BMI in long-standing IBD patients.