The aim of this study is to the effect of opioid (morphine) intradermal application on histaminergic and non-histaminergic itch. In particular, we would like to demonstrate that also peripheral administration of morphine may affect mast cell release of histamine.

Opioids (i.e. substances extracted from opium poppies, e.g. morphine) are used for treatment of both acute and chronic pain conditions as well as in surgical procedures. Opioids render effective pain relief, however, they may cause bothersome itch as a side effect. With this series of experiments, we wish to clarify how an injection with morphine in the skin layer called dermis (located right below the upper skin) will affect itch.

Inclusion Criteria:

• Healthy men and women
• 18-60 years
• Speak and understand English

Exclusion Criteria:

• Participants with any clinically significant abnormalities that in the opinion of the investigator may increase the risk associated with trial participation or may interfere with the interpretation of the trial results.
• Pregnancy or lactation
• Drug addiction defined as any use of cannabis, opioids or other addictive drugs
• Lack of ability to cooperate
• Current use of medications that may affect the trial such as antihistamines, antipsychotics and pain killers as well as systemic or topical steroids.
• Participants with known allergy/discomfort to the opioid morphine and antihistamine.
• Skin diseases
• Moles, scars or tattoos in the area to be treated or tested.
• Consumption of alcohol or painkillers 24 hours before the study days and between these
• Acute or chronic pain
• Participation in other trials within 1 week of study entry (4 weeks in the case of pharmaceutical trials)