Original sentence: " In most of their analyses they are able to state that there is no significant difference between melatonin and placebo; even the most common adverse events reported; headache, dizziness, nausea and drowsiness; did not significantly differ for melatonin vs.A similar analysis by the same team a year earlier on the efficacy and safety of exogenous melatonin in the management of primary sleep disorders found that: "There is some evidence to suggest that melatonin is effective in treating delayed sleep phase syndrome," and that evidence suggests that melatonin is safe with short-term use, three months or less.A systematic review in 2006 looked specifically at efficacy and safety in two categories of melatonin usage: first, for sleep disturbances which are secondary to other diagnoses and, second, for sleep disorders such as jet lag and shift work which accompany sleep restriction.As there are no regulated manufacturing standards in place, purity, safety and efficacy of the various melatonin products may not have been assessed.Melatonin is practically nontoxic and appears to exhibit almost no side effects in the short term, up to three months, when healthy people take it at low doses.Seventeen randomised controlled trials with 651 participants showed no evidence of adverse effects of melatonin with short term use.Some unwanted effects in some people, especially at high doses (~more than 3 mg/day) may include:  headaches, nausea, next-day grogginess or irritability, hormone fluctuations, vivid dreams or nightmares and reduced blood flow (see below).The study concludes: "There is evidence that melatonin is safe with short term use.These Canadian researchers found no trials showing evidence of effects on sleep onset latency in subjects with secondary sleep disorders or in subjects with disorders accompanying sleep restriction
Edited sentence: Administration is said to cause some unwanted effects in some people, especially at high doses (~more than 3 mg/day):  headaches, nausea, next-day grogginess or irritability, hormone fluctuations, vivid dreams or nightmares and reduced blood flow (see below).As there are no regulated manufacturing standards in place, purity, safety and efficacy of melatonin products may not have been assessed.Melatonin is practically nontoxic and appears to exhibit almost no side effects in the short term when healthy people take it at low doses