During Period 1 (double-blind treatment period), participants will receive an intramuscular (IM) injection of Debio 4126 once every 12 weeks over a total of 36 weeks (3 injections in total). Participants whose acromegaly is not well controlled may receive rescue medication.

Eligible participants (IGF-1 ≤1x ULN on Week 34) will enter Period 2 on Week 36 and receive an open-label Debio 4126 injection once every 12 weeks over a total of 24 to 60 weeks (between 2 and 5 injections in total). Participants with IGF-1 >1x ULN may receive rescue medication until Week 48, and may become eligible for Period 2 if their IGF-1 is ≤1x ULN.

During Period 1 (double-blind treatment period), participants will receive an IM injection of placebo once every 12 weeks over a total of 36 weeks (3 injections in total). Participants whose acromegaly is not well controlled may receive rescue medication.

Eligible participants (IGF-1 ≤1x ULN on Week 34) will enter Period 2 on Week 36 and receive an open-label Debio 4126 injection once every 12 weeks over a total of 24 to 60 weeks (between 2 and 5 injections in total). Participants with IGF-1 >1x ULN may receive rescue medication until Week 48, and may become eligible for Period 2 if their IGF-1 is ≤1x ULN.

During the Treatment Period, participants will receive an IM injection of Debio 4126 once every 12 weeks over a total of between 60 and 96 weeks (between 5 and 8 injections in total).

IM injection, a 12-week extended-release formulation of octreotide