It was once commonly used during PCT in the belief it will aid testosterone restoration, however this is flawed due to its mechanism of action. The drug mimics the effects of LH in the body, stimulating the Leydig cells to produce testosterone in the testes . This can be fruitful in rectify existing, or avoiding testicular atrophy on cycle. It will not aid the process of recovery in the post cycle phase however, as the drug will bring about heightened oestrogen levels due to the greater aromatising of the testosterone being produced in the testes , thus bringing about greater inhibition of the HPTA .
When examining a large dose (80mg) of melatonin given to healthy people in the morning (7:30am), the various parameters recorded were: a 24m half-life, with stable levels 60-150 minutes after ingestion and a gradual decline in serum melatonin levels until 9pm, when they returned to physiologically relevant levels.  The peak values were highly variable and significant in magnitude, 350-10,000fold higher than previously observed peak levels. Such variability has been seen elsewhere  ), and hourly dosing of 80mg melatonin was able to attenuate but unable to inhibit the decline throughout the day.