A prolonged-release depot suspension of microparticles containing the acetate salt of lanreotide, a synthetic peptide analog of the naturally occurring somatostatin, and copolymers. Lanreotide inhibits the secretion of growth hormone (GH) by binding to pituitary somatostatin receptors, and may inhibit various other hormones, including thyroid stimulating hormone (TSH) and the gastroenteropancreatic hormones insulin, glucagon and gastrin. This agent has a much longer duration of action than natural somatostatin and is selective towards the inhibition of growth hormone.