There is no supplement that will keep your endogenous test production up while on exogenous hormones, that is just not how the negative feedback loop of the hpta works. This is why we rum a pct, to recover these lower natural test levels after being suppressed. The best thing you can use on cycle is a test base, this will cover up the negative effects of suppression such as lethargy and loss of libido. Popular test bases are: 4 andro, dermacrine, epiandro, trest. All have their own unique properties so it depends on what your cycle is to decide what test base to use. These will actually make a huge impact on your cycle and are probably half the cost of hcgenerate. If you would like to discuss this further you are more than welcome to pm me with any questions.