Predominantly, studies of meditation report positive effects. However, some studies report that meditation may have adverse effects in certain circumstances (Lukoff, Lu & Turner, 1998; Perez-De-Albeniz & Holmes, 2000). If practiced improperly or too intensely, meditation can lead to considerable psychological and physiological problems. Serious, and credible teachers of meditation usually warn their students about the possible pitfalls of a contemplative path.

Another issue concerns the adaptation of eastern meditative concepts to a western culture, an adaptation that is often unfamiliar with the cultural matrix that the meditative concept originated from. Eastern concepts of meditation are often imported to a western setting within the popular context of new religious movements, or within the context of popular approaches to body and health. It is common for this popular context to be unfamiliar with the broad range of adverse affects that might occur during meditation, and to have limited tools for dealing with them when they do arise. Since the practice of meditation may include a powerful confrontation with existential questions, it is not considered wise to engage in intense meditation techniques without an extended period of psychological preparation, preferably in contact with a credible teacher or clinician. In the case of Asian contemplative traditions (Hindu, Buddhist), which has often originated within a monastic or reclusive context, there often exist major challenges connected to the way the particular meditation techniques are to be applied to a Western mindset without causing harm to the practitioner. For example passivity.

A growing body of clinical literature is now starting to address the phenomenon of meditation-related problems (Lukoff, Lu & Turner, 1998; Perez-De-Albeniz & Holmes, 2000). Several side-effects have been reported, including uncomfortable kinaesthetic sensations, mild dissociation and psychosis-like symptoms (Craven, 1989). From a clinical study of twenty-seven long term meditators, Shapiro (1992) reported such adverse effects as depression, relaxation-induced anxiety and panic, paradoxical increases in tension, impaired reality testing, confusion, disorientation and feeling 'spaced out'. The possibility that meditation might trigger strong emotional reactions is also reported by Kutz, Borysenko & Benson (1985). Therefore, meditation might cause serious side effects, even among long-term practitioners, and might even, in some instances, be contraindicated. The tendency of meditation to release unconscious material (Perez-De-Albeniz & Holmes, 2000) implies that the beginning meditator should approach the practice with moderation

Particularly in the Chinese Qigong tradition, stories of unguided practitioners or inexpertly guided students developing chronic mental and physical health problems as a result of their attempts at meditation training are not uncommon. English speaking practitioners and teachers of Qigong and related disciplines note that the practice of this contemplative exercise is sometimes accompanied by physical and psychological distress. The identification of this syndrome has led to the inclusion of a culture-sensitive category in the DSM-IV called Qi-Gong Psychotic Reaction (American Psychiatric Association, 1994: Appendix 1).

Meditative traditions which include the use of drugs are generally considered to be harmful to the practitioner. Additionally, as with any practice, meditation may also be used to avoid facing ongoing problems or emerging crises in the meditator's life. In such situations, it may be helpful to apply mindful attitudes acquired in meditation while actively engaging with current problems (see Hayes et al, 1999, chap. 3; Metzner, 2005).

Some modern methods of meditation do not include the use of drugs due to the known health problems associated with the use of some drugs. However, the use of stimulants has been proposed by some as a means to provide insight, and in some shamanistic traditions they are used as agents of ritual. Some Native American traditions for instance emphasized the smoking of a pipe containing tobacco or other plants. Some Hindu traditions use bhang, East Asian traditions use tea and Middle Eastern (and many Western) religions use coffee as an aid to meditation. During the 1960s, eastern meditation traditions and LSD became popular among many people, and many people suggested that LSD use and meditation were both means to the same spiritual/existential end. However, many people who had already been familiar with eastern traditions rejected this idea, including many who had tried LSD themselves. In The Master Game, de Ropp said that the door to full consciousness could be glimpsed through with the aid of substances, yet to pass beyond the door required yoga and meditation.