Vaginismus is a condition in which involuntary muscle spasm prevents vaginal penetration. Vaginismus occurs when penetrative sex or other vaginal penetration cannot be experienced without pain. Hegar dilators are used to treat vaginismus, also known as genito-pelvic pain disorder. The levator ani is the main pelvic floor muscle and painfully contracts during vaginismus. Awareness of vaginismus may not happen until vaginal penetration is attempted. Long-term opioid use can lead to decreased libido, delayed or absent ejaculation, and vaginismus. In some cases, vaginal penetration can be painful for older women (see, for example, vaginismus). It is combined with vaginismus into genito-pelvic pain/penetration disorder in the DSM-5. Strengthening the muscles that unconsciously tighten during vaginismus may be extremely counter-intuitive for some people. Vaginismus has been classified by Lamont according to the severity of the condition. A Cochrane review found little high quality evidence regarding the treatment of vaginismus in 2012.