Heh, just went to some websites on Opium
Opium can cause euphoria, followed by a sense of well-being and a calm drowsiness or sedation. Breathing slows, potentially to the point of unconsciousness and death with large doses. Other effects can include nausea, confusion and constipation. Use of opium with other substances that depress the central nervous system, such as alcohol, antihistamines, barbiturates, benzodiazepines, or general anesthetics, increases the risk of life-threatening respiratory depression.
And another site with personal experiences
It feels very mellow and dreamlike, euphoric
That Marx, he knew of what he spoke...........