Xorphanol is an opioid

Opioid

An opioid is a psychoactive chemical that works by binding to opioid receptors, which are found principally in the central and peripheral nervous system and the gastrointestinal tract...

 analgesic

Analgesic

An analgesic is any member of the group of drugs used to relieve pain . The word analgesic derives from Greek an- and algos ....

 from the morphinan

Morphinan

Morphinan is the base chemical structure of a large chemical class of psychoactive drugs, consisting of opioid analgesics, cough suppressants, and dissociative hallucinogens, among others.- Chemical Derivatives :Immediate derivatives of morphinan include:...

 family of drugs. It is a mixed agonist-antagonist at the μ-opioid

Mu Opioid receptor

The μ-opioid receptors are a class of opioid receptors with high affinity for enkephalins and beta-endorphin but low affinity for dynorphins. They are also referred to as μ opioid peptide receptors. The prototypical μ receptor agonist is the opium alkaloid morphine; μ refers to morphine...

 receptor

Receptor (biochemistry)

In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...

 and produces potent analgesic effects with little potential for dependence or abuse

Drug abuse

Substance abuse, also known as drug abuse, refers to a maladaptive pattern of use of a substance that is not considered dependent. The term "drug abuse" does not exclude dependency, but is otherwise used in a similar manner in nonmedical contexts...

.

Side effects in animal studies were relatively mild, with only sedation

Sedation

Sedation is the reduction of irritability or agitation by administration of sedative drugs, generally to facilitate a medical procedure or diagnostic procedure...

 and nausea

Nausea

Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...

 being prominent, although it also produced convulsions at the highest dose tested. However human trials revealed additional side effects such as headache

Headache

A headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...

s and euphoria

Euphoria (emotion)

Euphoria is medically recognized as a mental and emotional condition in which a person experiences intense feelings of well-being, elation, happiness, ecstasy, excitement and joy...

, and this was the subject of a lawsuit between the drug's inventors and the company to which they had licensed the marketing rights, which claimed that these side effects had not been revealed to them during the license negotiations. This dispute resulted in the drug never being marketed commercially, although it is still used in scientific research.