Psychedelics are a class of psychoactives whose primary effects are rooted in altering perception, causing a number of mental effects which manifest in many forms including altered states of consciousness, visual or tactile effects.
A difference between the common semantic and scientific uses of 'psychedelic' often occurs. Most psychedelic drugs are either tryptamines, phenethylamines or lysergamides, and these structural definitions often denote what constitutes a psychedelic proper. However, psychedelics are also part of a wider definition of 'hallucinogens,' which includes certain dissociatives and deliriants - these sharing in many of the typically 'psychedelic' effects of the classical psychedelic chemicals. While a drug may not be strictly classified as a psychedelic, it may share in the semantic definition of a substance which causes the user to experience extra-ordinary forms of consciousness through alterations in cognition and perception, forming 'the psychedelic experience.'
See List of Psychedelics for a full list.
The effects caused by psychedelics vary a lot depending on the particular substance, the dose and the set and setting of the trip. For example, stimulant effects are noted here (such as tension, slight increase in heart-rate) since many psychedelics are also somewhat stimulating, though these occur to different degrees depending on the particular chemical. See individual substance pages for more tailored effects.
Psychedelics may cause a wide range of visual effects, for an overview of these see Overview of Hallucinogenic Visuals.
Despite many common and prevalent misconceptions around psychedelic use, many psychedelics (including LSD and 2C-B) remain among the safest drugs in common recreational use, often with a very low potential for addiction. Some psychedelics, such as LSD, are almost impossible to physically overdose on, though others such as NBOMes have very low thresholds for overdose. However, regardless of the physical safety profile of the drug, it is always important to make sure the dose is within reasonable realms, since physical side-effects will increase with dosage, along with a greater risk of a bad trip or negative mental side-effects both during and following the trip.
The major physical dangers while on a reasonable dose of a psychedelic is the potential for an accident while the user undertakes an activity, occurring due to the shift in their perception. For example, a user on a psychedelic will likely not be able to safely or accurately judge distances as they would be able to sober. For this reason, it is important to avoid any activities which pose any threat or danger, or which require sober mental attention. Avoid driving and operating heavy (and probably light) machinery.
Psychedelics are known to potentially cause latent mental illness to manifest. Those with mental illnesses should not use psychedelics. Those with a family history of mental illness, including but not limited to depression, schizophrenia, and bipolar should use psychedelics with extreme caution, if at all.
During psychedelic trips, a 'bad trip' may be a possibility. This happens when the user enters a negative mindset, often find it difficult to shift their mind from a negative thought path (named 'thought looping'). The chances of a bad trip are increased depending on many factors, including the mental and emotional stability of the user or the setting of the trip - to mitigate these factors, only trip in a comfortable and positive environment.
The figure differs (such as with DMT and NBOMes), but many psychedelics have a physical tolerance lasting between 1-2 weeks. However, many users report a mental tolerance which may last longer than the physical tolerance, and increases in duration depending on frequency of use. Psychedelics are often considered to be heavy mental experiences, therefore it is always recommended to leave a reasonable amount of time (often a month or more) between trips, to avoid any adverse psychological effects of chronic use.
Many psychedelics are also somewhat stimulating, and therefore may cause similar side-effects to stimulants, particularly in high doses. These may include sweating, vasoconstriction and dehydration. Be aware of this, and remain hydrated.