Although electroconvulsive therapy is a low risk procedure with very few incidences of complications,[27] it inevitably brings some unwanted adverse effects. The most common side effects include general somatic complaints. However there also exists worry over cognitive impairment.[28]
Memory disturbances often receive the greatest concern when considering cognitive changes. These involve both anterograde amnesia (loss of ability to create new memories) and retrograde amnesia (loss of memory access to events before the ECT episode).[29] While anterograde amnesia often disappears days to weeks after completion of the ECT episode,[27] retrograde amnesia can persist for longer than four weeks and is often more for immediate time prior to ECT.[30] Indeed, retrograde amnesia may never completely resolve despite improvement during the first few months after ECT.[29] The memory of autobiographical information has been shown to be less affected by ECT than the memory of events of an impersonal nature.[31] It is also important to note that self-reports of retrograde amnesia tend to be more highly correlated with therapeutic outcome than with objective test results.[32]
The mode of delivery of ECT has an impact on the extent of memory impairment, and the UK ECT Review Group has identified some of these impacts. For example, bilateral ECT produces greater impairment than unilateral ECT. Treatment three times a week causes more impairment than bi-weekly treatment, and high dose ECT produces more impairment than low dose ECT. Despite discussion that sine wave treatment produces greater memory impairment than brief pulse, the evidence is too little and insignificant to be confirmed.
In addition to memory dysfunction, postictal (after seizure) disorientation and interictal (between seizures) confusion can also occur in patients.[28] While the former is experienced in all patients and lasts from a few minutes to hours, the latter happens occasionally and rapidly disappears over a period of days following completion of ECT.
The exact mechanism of how ECT leads to cognitive change is not fully understood. It was suggested that seizure induced during ECT can lead to neuronal atrophy in the hippocampus, however, no hippocampal atrophy or cell death was found in patients receiving ECT in a magnetic resonance spectroscopic imaging (MRS) study.[30]
Headaches, nausea and muscle soreness are frequent side effects of ECT and they usually last up to several hours.[28] Headaches are believed to be the result of superficial vasodilation whereas muscle pain is caused by the depolarising action of muscle relaxant used in ECT. They can be both managed with analgesics for prophylactic purpose.
Other less common side effects include cardiovascular complication (e.g. cardiac arrhythmias, ischaemia and hypertension), which can be the main cause of mortality and serious morbidity with ECT, and of adverse psychological reaction to ECT.[32]
Lastly, there is a small physical risk from having a general anaesthetic, with death or serious injury occurring in approximately 1 in 80000 treatments. As ECT is given in a course of treatments, the risk per course will be around 1 in 10 000.[33]
In conclusion, it is worth mentioning that when ECT is used, it usually bears the full burden of public fear of cognitive effects related to psychiatric treatment, as people often forget the fact that severe depressive illness and psychotropic drugs can also affect memory.[32] As a result, any detrimental effects should not be blamed solely on ECT.
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