According to NICE guidelines, fluoxetine is a first-line antidepressant for the management of depression in children and adolescents. There has been little discussion on urticaria occurring after 4 weeks on fluoxetine. Urticaria is defined as an itchy skin lesion "with localised oedema and is surrounded by redness which is also known as a wheal and flare phenomenon". In most urticarial scenarios, the trigger which is usually an allergen leads to an increase in levels of histamine among other chemicals into the skin.

We present the case of a 16-year-old young person with no previous history of skin conditions, who developed urticaria 4 weeks after starting fluoxetine for depressive disorder. No other trigger could be identified. On discontinuing fluoxetine, the rash gradually declined over time and completely resolved ten days later. On further enquiry, the patient reported eating at least one chocolate bar a day. He did admit to receiving a large amount of chocolate just before the rash began and hence was possibly eating more than his usual amount at the time. Furthermore, the rash occurred at the point when steady-state levels of fluoxetine were believed to have just been reached.

Adverse effects of medication have always been a challenging part of managing patients. Although rash that develops acutely after starting fluoxetine has been published so far, literature on rash that develops after 4 weeks on treatment is limited. Cederberg et al (2004) and Gahir (2021) described the association of SSRIs (fluoxetine and sertraline) and chocolate (which contains serotonin) leading to an itchy hive-like rash. In these cases, discontinuation of the SSRI and use of antihistamine led to a resolution of symptoms.

We report a case who developed urticaria 30 days on fluoxetine without any other identifiable triggers. Aspects of this case to support a possible rash caused by chocolate-fluoxetine interaction include the rash occurring when the patient was consuming chocolate (quantities possibly increased immediately prior to the onset of rash), rash occurring when steady-state levels of fluoxetine had just been reached, no other identifiable trigger to explain the rash in the history and the slow resolution of the rash which can be explained by the long half-life of fluoxetine.

This report highlights the importance of being mindful of this rare dermatological side effect of fluoxetine despite it occurring weeks after initiation. Patients should also be made aware of this possible side effect and its association with consuming chocolate.