Infantile spasms (West's Syndrome) is a syndrome which includes a peculiar type of epileptic seizure, the spasms, and an electroencephalogram (EEG) abnormality often called hypsarrhythmia. Psychomotor retardation is frequently found at follow up. Approximately two thirds of affected infants will have a detectable underlying neurological abnormality, but still little is known about the pathophysiological basis for infantile spasms and treatment remains problematic.To compare the effects of single pharmaceutical therapies used to treat infantile spasms in terms of control of the spasms, resolution of the EEG, relapse rates, psychomotor development, subsequent epilepsy, side effects, and mortality.Published data: Cochrane Epilepsy Group Specialised Register, CENTRAL (The Cochrane Library 2007, Issue 4), MEDLINE, EMBASE, and the reference lists of all retrieved articles.Unpublished data: ISRCTN Register (www.controlled-trials.com), correspondence with colleagues and drug companies, and requests at international conferences.All randomised controlled trials of the administration of drug therapy to patients with infantile spasms.Data collection from all relevant publications was independently undertaken by three review authors using a standard proforma. Analysis included assessment of study quality and looking for sources of heterogeneity.We found 12 small RCTs (less than 60 patients enrolled) and two larger RCT (more than 100 patients enrolled). These 14 studies looked at a total of 681 patients treated with a total of nine different pharmaceutical agents. Overall methodology of the studies was poor, partly because of ethical dilemmas such as giving placebo injections to children. Two studies showed that placebo was not as good as active treatment in resolving the spasms. The strongest evidence suggested that hormonal treatment leads to resolution of spasms faster and in more infants than does vigabatrin. Responses without subsequent relapse may be no different. The same study suggests that hormonal treatments (prednisolone or tetracosactide) might improve the long-term developmental outcome compared with vigabatrin in infants not found to have an underlying cause for their infantile spasms.To date, there have been few well-designed RCTs that considered the treatment of infantile spasms, and the numbers of patients enrolled have been small. Overall methodology has been poor, hence it is not clear which treatment is optimal in the treatment of this epilepsy syndrome. Hormonal treatment resolves spasms in more infants than vigabatrin but this may or may not translate into a better long-term outcome. If prednisone or vigabatrin are used then high dosage is recommended. Vigabatrin may be the treatment of choice in tuberous sclerosis. Resolution of the EEG features may be important but this has not been proven. Further research using large studies with robust methodology is still required.