This book investigates the stories of six African plants (periwinkle, pennywort, grains of paradise, Strophanthus, Cryptolepis and Hoodia) and their introduction to the global pharmaceutical industry in the twentieth century. It is based on first-hand interviews and on extensive archival investigation in Ghana, Madagascar, South Africa and the US. The stories around the six plants are all extremely intriguing, and the author has carried out impressive and original historical and anthropological work. The book's primary focus is on the relationship between Africa and the West, positioning itself in post-colonial and postmodern historiography rather than in world history – approaches distinguished by C.A. Bayly in the introduction to his The Birth of the Modern World (2003). Thus Osseo-Asare follows most of the recent works in the history of science concerning the circulation of knowledge between centre and periphery, which aim to contest the well-known theses in Bruno Latour's Science in Action (1986). Thus it comes as no surprise that one of the main concerns of Bitter Roots is to establish whether and how the Africans should be compensated for the Western exploitations of plants which naturally grow in Africa. In the conclusion, the author introduces the notion of bioprosperity ‘to identify an approach for sustaining plants, pharmaceuticals and people with relationships of equity’ (p. 202), and suggests some concrete measures to improve bioprosperity. These mainly consist of mapping the distribution of herbal knowledge and promoting the redistribution of revenues, by means of biodiversity trust funds, class-action suits against pharmaceutical companies, and the attribution of a sort of protected designation of origin for African plants along the lines of the European Union scheme protecting regional products, such as Parmesan cheese and French champagne.

The post-colonial approach leads the author to focus on letting the subaltern speak, allowing her to highlight the importance of gender and the complexity of the relationships between healers and African researchers in her narrative. Indeed, the author explains how the introduction of the grains of paradise to the treatment of impotence reveals the Western male appropriation of a remedy used in Africa by women. Collaboration between Canadian researchers and Congolese researchers was crucial in this gender transformation of the plant. Another interesting case is that of a drug based on the extraction of an alkaloid from Cryptolepis, a plant already used by healers in Ghana, which proved to be effective against malaria. The author highlights the strategies on patents and publications developed by Ghanaian researchers in order to gather resources for their investigations.

The post-colonial focus, however, causes some troubles for the book. Indeed, the author's claim that the search for new drugs was a central component of colonial expansion in Africa during the nineteenth century should be reversed: Western innovation networks focused on drugs apt to fight tropical diseases, because of the colonial expansion. The time and resources spent by German, British and French innovation networks finding drugs effective against tropical diseases such as yellow fever, sleeping sickness and malaria, which (apart from malaria in certain regions of France) were not a major concern in those countries, is otherwise not comprehensible.

This remark leads directly to the second major concern with the book: the role played by patents and by multinational and Western pharmaceutical companies. In the case of periwinkle, it was a method for extracting the alkaloid that was patented. However, the plant continued to be sold in local and regional African markets. Periwinkle was cultivated in Ghana, although it naturally grows elsewhere and even in certain southern areas of the US. On this view, the patent on the extraction process did not protect the interests of the firm against local farmers and merchants, but against global industrial competitors. The same argument works for the case of the grains of paradise, in which the African local and regional market and the global industrial market did not seem to be in competition, as the grains of paradise was marketed in the former as a female remedy and in the latter as a male one. In other cases, a closer look at the global industrial and geopolitical contexts would have likely allowed the author to answer the questions raised by her own investigation. This is the case with Strophantin, a drug based on an alkaloid extracted as arrow poison used by a number of African people in Gambia and Cape Verde. The alkaloid was extracted by a Scottish researcher, Fraser, and was marketed as a drug for poor blood circulation, having effects comparable with those of Digitalin. However, the British dismissed its production in 1922 and plantations of Strophanthus set up by the British in Africa were destroyed. The demise of the Strophanthus business is ascribed by the author to the worries of the colonial authorities about securing the cultivation of a potential poison among the natives. The author looks at this story as an example of appropriation of African expertise by colonial authorities. However, the Africans did not use Strophanthus as a drug, but as a warfare poison. Neither is it clear why the British did not try to cultivate Strophanthus elsewhere. In the case of Cryptolepis, it is not clear why no medical investigators and pharmaceutical companies pursued research on it, after the publication in international journals of research that seemed to prove its high effectiveness against malaria.

Despite these issues, the book is an important contribution to the history of the circulation of African medical plants, and of the relationship between African medical investigators and healers, and is a worthwile read for anyone who is interested in the colonial and post-colonial dimension of the twentieth-century relationships between African bio-medical researchers and Western innovation networks.