Marijuana (Cannabis sativa L.) and its derivatives have been used both medicinally and recreationally for at least fifty centuries. However, the chemical structure of their active components – the cannabinoids – was not elucidated until the early 1960s. Pharmacological studies conducted at that time led to the conclusion that, among all the cannabinoids present in the plant, one of them, D⁹-tetrahydrocannabinol (THC), was especially relevant owing to its high abundance and potency. Three decades later, the mechanism of THC action was unravelled. Thus, in the early 1990s it was found that THC acts on our body because it is similar to (and therefore mimics the effects of) a family of molecules produced by our organism that were so called endocannabinoids -anandamide and 2-arachidonoylglycerol being their main representatives. THC and endocannabinoids act by engaging specific proteins located on the surface of our cells and called cannabinoid receptors, two of which have been well characterized: CB₁ y CB₂. Nowadays it is known that these receptors, especially the former, are expressed preferentially in areas of the central nervous system that control processes such as motor behaviour, memory and learning, pain, appetite, nausea and vomiting, emotions and sensorial perception, which obviously explains that these processes are modulated by both the endocannabinoids generated at those locations and the THC that gains access to them owing to cannabis consumption. Cannabinoid receptors are also present at many other sites in our body, for example the peripheral terminals that innervate the skin and the digestive, circulatory and respiratory tracts, as well as in the immune system, the reproductive organs, the eye and the vascular endothelium. All these discoveries have contributed not only to an extraordinary expansion of the basic knowledge on how cannabinoids act in our body, but also to the renaissance of the study of their therapeutic properties, that constitutes a current topic of debate with ample scientific and clinical consequences.

In this context, by 1995 our research group started to study the molecular mechanisms by which endogenous and plant-derived cannabinoids act in the body. Specifically, our interest focused on unravelling whether these compounds impact cell generation, growth and survival, not only in the nervous system but also in other tissues. Understanding these processes is a pivotal issue for characterizing the aetiology and progression of neurodegenerative diseases (characterized by a loss of neural cells) and oncologic processes (characterized by an uncontrolled cell proliferation) and, therefore, for designing rational therapies for their treatment. Along these years we have observed for example that, upon activation of their specific receptors, cannabinoids modulate key cell signalling pathways, thereby eliciting effects such as progenitor cell generation, neuron and glial cell survival, and, on the contrary, apoptosis of brain, breast, skin and pancreatic cancer cells. These cellular events have a clear physiological relevance in laboratory animals, in which we have observed that cannabinoids, for example, control brain development, contribute to the regeneration and protection of nervous tissue upon damage, and inhibit the growth of malignant tumours. Overall, these studies support the notion that cannabinoid receptors are involved in the control of basic cell decisions and may thus constitute new pharmacological targets. However, further basic and preclinical research as well as thorough clinical trials are required to allow us to know whether cannabinoids could be used – aside from their palliative actions – as therapeutic agents in the treatment of neurodegeneration and cancer.