As far as I know, psychologists have speculated for a long time about the long-term effects of abstinence from sex and of sexual frustration. Some of them, including Wilhelm Reich (I think), have claimed that such abstinence has negative impacts. I wonder how the apparent happiness of Buddhist monks can be explained by such theories. Of course, one may question if they are really happy. But it is often said by observers that monks are cheerful people (see, for example, Professor Richard Davidson's descriptions). And Gautama Buddha, the founder of Buddhism, claimed that his teachings aimed liberation from suffering. In his view, suffering is caused by craving and attachment.
At least since the 20th century, western psychologists have shown interest in Buddhism. One can here name like Erich Fromm and Carl Jung, among others, as psychologists who have written positively about Buddhism.