Although many of meditations adverse effects reported in literature are anecdotal cases studies, incidental findings or unexpected outcomes it is clear that meditation is not a universally benign intervention and that it can be associated with both serious and non-serious adverse reactions. Some studies, such as those of Otis (1984) and Persinger (1993, 1992), suggest a dose response relationship whereas others, such as that of Xu (1994), suggest an unpredictable idiosyncratic effect.
For more information regarding future research that needs to investigate the adverse effects of meditation, check Dr Ramesh Manocha’s blog.