As @sempaiscuba points out in a comment, the source cited for that statement on Wikipedia is "The Religious and Medicinal Uses of Cannabis in China, India and Tibet" by Mia Touw and the full text is available. Here is the relevant quote:
Though little has been written on the use of cannabis in the Himalayas and the Tibetan plateau, no doubt due to the inaccessibility, of the region for study, there are clear indications that the plant is more highly valued and more consistently used there than anywhere else. It was traditionally considered sacred in Tibet (Aldrich 1977). [...] In Tantric Buddhism, which flowered in the Tibeto-Himalayan region, cannabis is an important part of the meditative ritual which may or may not include sexual intercourse. It is taken to facilitate the meditation and heighten awareness of all aspects of the ceremony. The large dose, taken orally, is timed so as to ensure increasingly heightened awareness from the beginning of the ritual onwards, with the greatest "high"-delayed when taken orally by about an hour and a half-coinciding with the climax of the ceremony (Bharati 1965).
Tantric cannabis use in India rose in about the 7th century A.D. in an explosive mingling of the doctrines and practices of Shaivite Hinduism and Tibetan Buddhism. Tantrism reached its height in medieval Bengal and the Himalayan kingdoms...
The substance of the text and rituals described in the article are more Hindu than Buddhist but it is suggested that cannabis use in Tantric ritual had at least some influence on Buddhism, in Nepal and Tibet. The PDF of the Bharati text is not OCRd to copy/paste from, but it similarly seems to be thin on evidence that ritual cannabis use was a major part of Buddhism, as opposed to Hinduism. All of these texts are referring to an early period where the distinction between the two traditions was not yet strong.