A composition for treating osteoporosis comprising Acroceras macrum gold nanoparticles (AM-AuNPs). The composition is prepared by mixing an Acroceras macrum extract with an aqueous chloroauric acid (HAuCl4) solution to provide a mixture including the Acroceras macrum gold nanoparticles; removing unreacted Acroceras macrum extract from the mixture followed by purifying the Acroceras macrum gold nanoparticles; and obtaining the gold nanoparticle composition comprising the Acroceras macrum gold nanoparticles (AM-AuNPs). The composition may be used to form drug compositions for treating osteoporosis.