Codeine: C18H21NO3

Codeine is a Isoquinoline alkaloid

Codeine is metabolized in the body to morphine but is far less habit forming than morphine and only a very small portion of the codeine is converted. Codeine is an effective analgesic but only in small doses. If the dosage is increased it increases the side effects without any significant increase in the therapeutic effect of the drug.
Codeine is antitussive, analgesic and narcotic.
Side effects of codeine can be nausea, constipation, drowsiness and urinary retention. Overdose can cause respiratory failure and death.

Isoquinoline Alkaloids: A large class of medically active alkaloids with very varied properties although this group does contain many constituents from which the most habit forming drugs are made. Precursors of isoquinoline alkaloids are tyrosine and phenylalanine.

Properties of these alkaloids range widely from Anti-inflammatory, antifungal, antitumor, antimicrobial and antiviral to analgesic, narcotic and antitussive, plus virtually everything in-between. Because of this very wide scope each of the alkaloids should be regarded as individual and no general properties can be attributed to the group known as isoquinoline alkaloids.

Alkaloids Typical alkaloids are alkaline organic vegetable substances containing one or more nitrogen atoms. This nitrogen base is capable of combining with acids to form crystalline salts. Most alkaloids are derived from amino acids while a few are derived from isoprene units. Alkaloids are white or colourless solids containing oxygen (oxygen free alkaloids are few and far between and then can only exist as liquids) Most alkaloids are not water soluble, extraction is normally by tincture.
Alkaloids are found in about one quarter of all flowering plants. Thousands of alkaloids have been identified from a large number of plants where the alkaloid can be present in virtually every part of the plant or just a specific part like rhizome, leaf or seed.
Alkaloids generally have profound physiological impact on the human body and nervous system effects are predominant.
Many alkaloids are used as extracted and refined compounds derived from the actual plants or synthesised compounds in pharmaceutical drugs.
Several Alkaloids are banned in many countries because of the extreme impact on the nervous system (strychnine for instance is a deadly poison in very small doses) and the habit forming nature of some of the alkaloid compounds.