Hi, Thanks for writing in to us. Desvenlafaxine (brand name: Pristiq), also known as O-desmethylvenlafaxine, is an antidepressant of the serotonin-norepinephrine reuptake inhibitor class. Efficacy is an important factor to consider because it reflects the ability of the drug to produce the desired effect; hence, the higher the efficacy, the better the results. Expired medication may not adequately treat minor conditions (for example, minor headache, cold), or serious conditions (for example, diabetes or heart disease) because of reduced efficacy. As a consequence, inadequate relief from sickness could eventually lead to longer sick days, increased absences from work/school, and lost productivity at work/school. The safety of expired medications should also be considered. Medications may change their chemical and physical properties, as is evident when tablets disintegrate and liquids separate into layers, or even change color within the dispensed bottle. As can be seen, the big issues with expired medications are two-fold: drugs become weak and may potentially be unsafe. It is advisable to discard all expired medications. Hope this helps