Serious reactions include those that are:-

Blood
Bone marrow dyscrasias
Coagulopathies
Haemolytic anaemias

Cardiovascular
Arrhythmias
Cardiac arrest
Cardiac failure
Cardiomyopathy
Circulatory failure
Hypertension
Hypotension
Myocardial
Ischaemia/infarction
Sudden death

Central nervous system
Anorexia nervosa
Catatonia
Cerebrovascular accident
Coma
Confusional state
Dependence
Depression
Epilepsy (inc. exacerbations)
Extrapyramidal reactions
Hallucinations
Hyperpyrexia
Intracranial pressure
Myasthenia
Neuroleptic malignant
Neuropathy
Psychosis
Withdrawal syndrome

Gastrointestinal
Colitis
Haemorrhage
Hepatic cirrhosis
Hepatic dysfunction
Hepatic fibrosis
Ileus
Pancreatitis
Perforation
Peritonitis (inc. fibrosing)
Pseudo-obstruction

Immunological
Anaphylaxis
Arteritis
Drug fever
Graft rejection
Lupus syndrome
Polyarteritis nodosa
Vasculitis

Malignancy
Any

Metabolic
Acidosis
Adrenal dysfunction
Diabetes
Hypercalcaemia
Hyperkalaemia
Hypokalaemia
Hyponatraemia
Pituitary dysfunction
Porphyria
Thyroid dysfunction

Musculoskeletal
Arthropathy
Aseptic bone necrosis
Osteomalacia
Pathological fracture

Respiratory
Alveolitis (allergic, fibrosing)
Bronchospasm
(inc. exacerbation)
Pneumonitis
Respiratory failure
Thromboembolism

Skin
Angioedema
Bullous eruptions
Epidermal necrolysis
Exfoliation (generalised)

Special senses
Cataract
Corneal opacification
Glaucoma
Hearing loss
Vestibular dysfunction
Visual loss