Mobile phone short messaging service (SMS) reminders may be a low-cost method for promoting medication adherence. Our objective was to determine whether text SMS reminders improve medication adherence in patients with bipolar I disorder even after discontinuation of the intervention. Participants were stable adult bipolar I disorder outpatients on maintenance medication who were randomized to receive treatment as usual (TAU; n = 70) or TAU plus twice-weekly medication reminders by SMS (n = 62) for 3 months. Rater-blinded assessments of medication adherence, treatment attitudes, and quality of life (QoL) were obtained at baseline, at the 3-month intervention endpoint, and at a 3-month post-intervention follow up during which both groups received TAU. Intent-to-treat analyses were conducted on the full randomized sample. The clinical trial protocol was registered with the Clinical Trials Registry of India (CTRI) (CTRI/2016/07/007101). The SMS intervention improved medication adherence and attitudes towards medication at the end of the treatment phase; these benefits were maintained for medication adherence but not for attitudes towards medication at the end of the follow-up phase. The SMS intervention did not improve QoL outcomes. These findings indicate that biweekly SMS reminders improve medication adherence and the benefits persist for at least 3 months after the SMS reminders are discontinued. The SMS reminders do not affect attitudes towards treatment or QoL.