Muscle relaxation from Diphenhydramine

Muscle relaxation can be described as the experience of muscles throughout the body losing their rigidity and tension while becoming noticeably relaxed, loose, and comfortable. This effect involves a palpable softening of muscular tightness that many people carry unconsciously during everyday life, particularly in areas such as the shoulders, neck, jaw, and lower back. The sensation is generally experienced as deeply pleasant and physically soothing.

At lower intensities, muscle relaxation manifests as a subtle loosening of tension that one may not immediately notice unless they direct their attention to it. Muscles that were previously tight or sore may feel slightly more comfortable, and there is a general sense of physical ease. At higher intensities, the effect becomes a profound and encompassing sense of bodily relaxation in which every muscle group feels completely slack and free of tension. This can result in a heavy, sinking sensation as if the body is melting into whatever surface it is resting on.

This effect is particularly useful for those who are currently experiencing muscle spasms, chronic pain, hyperreflexia, or the physical tension that accompanies anxiety and stress. Many people who experience substance-induced muscle relaxation report that they were not fully aware of how much tension they were carrying until the effect made the contrast apparent. The relief can be especially pronounced in individuals who suffer from conditions involving chronic muscular tightness.

Muscle relaxation is most commonly induced under the influence of moderate dosages of depressant compounds such as benzodiazepines, barbiturates, GHB, and other GABAergics. It also occurs prominently with opioids, skeletal muscle relaxants like carisoprodol and cyclobenzaprine, and cannabinoids. Certain psychedelics, particularly those with body-load characteristics, can produce muscle relaxation as part of their physical effect profile, though this varies considerably between substances.

Muscle relaxation is often accompanied by other coinciding effects such as sedation, anxiety suppression, pain relief, and physical euphoria. The combination of these effects frequently contributes to the overall sense of comfort and well-being that characterizes the experience of many depressant substances. However, at very high intensities, excessive muscle relaxation can contribute to motor control loss and respiratory depression, particularly with GABAergic substances and opioids.