Opiates

The term "opiate" is used in different ways in medical literature. In the narrower sense, it includes psychoactive substances that are obtained directly from the milky sap of the opium poppy (Papaver somniferum). This mainly contains morphine (approx. 3 - 23 %) and codeine (approx. 0.2 - 3.5 %). Other natural alkaloids of opium are:

• noscapine
• papaverine
• thebaine

In pharmacology, the term "opiate" is usually used for opium alkaloids and the semi-synthetic and non-peptide drugs derived from them.

In clinical usage, however, the term "opiates" is also used as a synonym for the term"opioids". This equivalence is rejected by many pharmacologists.

In narcotics law, the term opiate is mainly used in connection with opiate addiction for opioids with a dependency potential.

A distinction is made between different types of opiates:

• the full agonists (e.g. morphine and heroin) with addictive effects.
• full antagonists(opioid receptor antagonists) (e.g. nalorphine and naloxone), which are also inhibitors of adenylate cyclase but do not stimulate the synthesis of these enzyme molecules (antagonists have an analgesic effect but are not addictive). They do, however, induce anxiety, aggression, and hallucinations).
• Partially agonistic/antagonistic substances that act, for example, agonistically at κ-opioid receptors (see opioid receptors below) and antagonistically at μ-opioid receptors. Such dualistically acting compounds are used as analgesics in the same way as the full agonists.

Morphine is the oldest and most important opiate and is considered the reference substance in pain therapy against which the analgesic effect of all opiates and opioids is measured. For example, a therapeutic potency of 2 means that only 50% of the dose that would be required if morphine were used is needed.

Of the opioids, morphine remains the most relevant. In recent decades, other opioids (e.g., oxycodone, hydromorphone, fentanyl) have become more important in pain medicine.

All opioids have a uniform basic structure. They bind to opiate receptors (opioid receptors) and also inhibit the enzyme adenylate cyclase. Opiates are effective even in very low concentrations and have a pain-suppressing effect.

In addition, they reduce mental activity (sedative effect), eliminate feelings of conflict and anxiety (tranquillising effect), have a euphoric effect and inhibit the respiratory and coughing centres. With repeated use they lead to the development of tolerance.

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