Here we provide the updated version of the guidelines of the European Association for Palliative Care (EAPC) on the use of opioids for the treatment of cancer pain. The update was undertaken by the European Palliative Care Research Collaborative. Previous EAPC guidelines were reviewed and compared with other currently available guidelines, and consensus recommendations were created by formal international expert panel. The content of the guidelines was defined according to several topics, each of which was assigned to collaborators who developed systematic literature reviews with a common methodology. The recommendations were developed by a writing committee that combined the evidence derived from the systematic reviews with the panellists' evaluations in a co-authored process, and were endorsed by the EAPC Board of Directors. The guidelines are presented as a list of 16 evidence-based recommendations developed according to the Grading of Recommendations Assessment, Development and Evaluation system.
Low levels of serotonin , a neurotransmitter in the brain, have been linked to depression . High levels of estrogen, as in first-generation COCPs, and progestin, as in some progestin-only contraceptives, have been shown to lower the brain serotonin levels by increasing the concentration of a brain enzyme that reduces serotonin. This observation, along with some small research studies  have inspired speculation that the pill causes depression. In 2016, a large Danish study of one million women showed that use of COCPs, especially among adolescents, was associated with a statistically significantly increased risk of subsequent depression, although the sizes of the effects are small (for example, % of the women who took any form of oral birth control were prescribed anti-depressants for the first time, compared to % of women in the control group).