Sourced from: http://www.webmd.com/mental-health/addiction/drug-overdose#1
So what could be the reason why some people just don’t follow the doctor’s advice and instead go it their way? Well it is said that there are some medications that meddle with how your mind works and therefore making them susceptible to abuse.
Some medications have psychoactive (mind-altering) properties and, because of that, are sometimes abused—that is, taken for reasons or in ways or amounts not intended by a doctor, or taken by someone other than the person for whom they are prescribed.
Commonly abused classes of prescription drugs include opioids (for pain), central nervous system (CNS) depressants (for anxiety and sleep disorders), and stimulants (for ADHD and narcolepsy).
Sourced from: https://www.drugabuse.gov/drugs-abuse/prescription-drugs-cold-medicines
Sourced from: http://www.emedicinehealth.com/drug_overdose/page4_em.htm#what_is_the_treatment_for_a_drug_overdose