On poisons in particular he speedily became a high authority; his well-known treatise on them was published in 1829, and in the course of his inquiries he did not hesitate to try such daring experiments on himself as taking large doses of Calabar bean (Physostigmine).
Robertson made several contributions in the field of ophthalmology; in 1863 he researched the effects on the eye made by physostigmine, an extract from the Calabar bean (Physostigma venenosum), which is found in tropical Africa.