後期的印度密教即怛特羅佛教，也就是所謂的金剛乘佛教。除了運用身心複合體的氣．脈．明點進行精神．生理學上的操作之外，還配合人類身體的小宇宙，與外在世界（視為佛．菩薩示現者）的大宇宙之合一；藉助於曼荼羅是宇宙圖，身體亦是宇宙的縮圖，故以曼荼羅作為媒介，為了與佛的神祕合一體驗，獲得菩提、成就佛果。毫無疑問地，金剛乘的身體論多少受到濕婆教的影響，不過在存在論上、認識論上、或在修行方法上兩者都是截然不同的。要從事瑜伽與怛特羅的修持，必須有極高的智力。所以它不是適合所有的人，事實上也是如此的。瑜伽與怛特羅只適合一些得天獨厚具有高度知性的教養與能力者。故西藏佛教的上師說，金剛乘的修持成佛容易，墮入地獄也容易。吾人不可不慎！

The later Indian Esoterism or Tāntric Buddhism, is also called Vajrayāna Buddhism. It must exert breath (rlung, Skt. prāṇa), channels (rtsa, Skt. nāḍī) and drops (thig le, Skt. bindu) of the psycho-physical complex; besides these (psycho-physiological operations), Vajrayāna also adopts that homology of macrocosm and microcosm. The former signifies the external worlds out of the emanations of the Buddhas and the Bodhisattvas, while the latter indicates the mirror of the universe, or the human body. Maṇḍala is a cosmogram; hence the human body is the epitome of the universe. Through visualizing maṇḍala, it brings to the aim of the experience of mystical identification with the Buddhas, and then, it comes to attain enlightenment (byang chub, Skt. bodhi), meanwhile achieving Buddhahood (sangs rgyas kyi go 'phang, Skt. buddhatva).Surely the human body theory of Vajrayāna had been influenced by the Śaiva Schools (Śivaism), more or less. But in terms of ontological, epistemological or practical methods, there are totally different. It is clear that the highest degree of intellectual power is necessary to follow the path of Yoga (especially Haṭhayoga) and Tantra (Anuttarayoga), and that it cannot be, and, in fact, never was, meant for all. Yoga and Tantra were meant only for a few fortunate persons who were blessed with a high degree of intellectual refinement and power. As mentioned above, I often remember the Tibetan Master's saying, ”Practicing Vajrayāna is easy to achieve Buddhahood, but also easy to sink into the underworld (dmyal ba, Skt. naraka).” So all of us must be careful!