For moderate to severe morning sickness and hyperemesis gravidarum: In the UK, promethazine is drug of first choice, being preferred as an older drug with which there is a greater experience of use in pregnancy (second in line being metoclopramide or prochlorperazine). For allergies such as hay fever and together with other medications in anaphylaxis
To aid with symptoms of the common cold
Motion sickness, including space sickness
Hemolytic disease of the newborn
Anxiety before surgery

Side effects
Some documented side effects include:

Tardive dyskinesia, pseudoparkinsonism, acute dystonia (effects due to dopamine D2 receptor antagonism)
Confusion in the elderly
Drowsiness, dizziness, fatigue, more rarely vertigo
Known to have effects on serotonin and dopamine receptors. Dry mouth
Nausea
Respiratory depression in patients under age of two and in those with severely compromised pulmonary function
Blurred vision, xerostomia, dry nasal passages, dilated pupils, constipation, and urinary retention. (due to cholinergic effects)
Chest discomfort/pressure (In children less than 2 years old)
AkathisiaLess frequent:

Cardiovascular side effects to include arrhythmias and hypotension
Neuroleptic malignant syndrome
Liver damage and cholestatic jaundice
Bone marrow suppression, potentially resulting in agranulocytosis, thrombocytopenia, and leukopenia
Depression of the thermoregulatory mechanism resulting in hypothermia/hyperthermiaRare side effects include:

SeizuresBecause of potential for more severe side effects, this drug is on the list to avoid in the elderly. In many countries (including the US and UK), promethazine is contraindicated in children less than two years of age, and strongly cautioned against in children between two and six, due to problems with respiratory depression and sleep apnea.Promethazine is listed as one of the drugs of highest anticholinergic activity in a study of anticholinergenic burden, including long-term cognitive impairment.
Tanapox (a virus from the genus Yatapoxvirus) was first seen among individuals in the flood plain of the Tana River in Kenya during two epidemics (1957 and 1962) of acute febrile illness accompanied by localized skin lesions. Signs and symptoms
The incubation period in human cases remains unknown, but in a person who underwent voluntary inoculation, erythema and central thickening appear by the fourth day. Most patients present a mild pre-eruptive fever that lasts 3–4 days, severe headaches and backaches, and often itching at the site where the skin lesion develops.There is initially a small nodule, without any central abrasion. This small nodule soon becomes papular and gradually enlarges to reach a maximum diameter of about 15 mm by the end of the second week of infection. The draining lymph nodes are also enlarged and tender from about the fifth day following the appearance of the skin lesion. The lesion remains mostly nodular but, ulcerates during the third week and then gradually heals within five to six weeks, leaving a scar. In Kenya, the lesions were almost always solitary and were found on the upper arm, face, neck, and truck. Conversely, in Zaire, 22% of patients had multiple lesions, usually two or three. The maximum number of lesions seen in one patient was ten. In the case of Zairian patients, the lesions were mostly found on the lower limbs, with a couple of patients reporting lesions on the upper limbs, trunk, and head.