Testosterone is probably the single most potent sexual enhancer bar none. In both men AND women. It is the reason why men wake-up with erections every morning (testosterone is produced while a man sleeps and tapers off through the day) and why women (generally) become hornier as they get older (their hormonal balance shifts in favour of testosterone).
It is responsible for the cascade of hormone/neurotransmitter release that stimulates spermatogenesis, erections, arousals, drive, motivation....
Along with its metabolite DHT, it works directly to stimulate the sexual repsonse in both males and females. The mechanism is too complicated to discuss here - suffice to say, it has pro-sexual effects on the penis, prostate, testicles - and their corollaries on the female body.
There are various supplements that boost testosterone, however the only ones with any scientific backing are Tongkat Ali, and Maca.
Other popular supplements such as Tribulus have no androgenic effects, stimulating the sexual response through the NO mechanism - which can easily be replicated by eating lots of protein. Nor does ZMA - a popular bodybuilding supplement.
Zinc does not stimualte testosterone either, though it is a constituent of semen and so has its own libido enhancing mechanism.
However, NONE of these supplements will come close to the power-punch you will get injecting synthetic testosterone and its various esters.
These are mailny but not exclusively: test suspension, test propionate, test enanthate, test cypionate. Each ester has a different half life, with the longer half life esters staying in your body longer and exerting their effects longer. Alkylated oral test doesn't have the same effect, you need liquid test injected.
For example, test suspension has a half-life of 4-8 hours (the shortest). Inject 100mg of this and you'll feel like someone put fire up your arse. Your sexual arousal state will be uncontrollable - men AND women. And within that 8 hours, you'll feel like you can go again and again fucking anything that walks.
But - as always - there's numerous downsides. As an anabolic steroid, testosterone is a dangerous substance if not handled with care.
For men, within a week (depending on volume) it will shut down your bodies natural production of testosterone. Your balls will shrink to tiny marbles. Also, with all that test in your system, your body will begin to convert large quantities into oestrogen. This will flood your system and virtually shut down your libido to zero. You will also develop bitch tits, accelerate hairloss, have bouts of uncontrollable acne. For women, your clitoris will grow to resemble a small penis, your voice will deepen, and you will grow facial hair. This is mailny due to testosterones androgenic qualities.
For women i would advice AVOIDING injectible testosterone altogether - not worth the long-term risks IMO. Rather, opt for the testosterone patches that are available on the market - far safer, lower doses. For men, the negative effects listed here can EASILY be avoided. Using aromatise-inhibitors to prevent the conversion of test to estrogen, SERMS to block the bitch-tits, and injections of HCG to prevent the shrinkage of balls. Of course these methodologies are too complex to go into here - so anyone wanting to use test MUST do as much research as you can on a bodybuilding site where you will be advised exactly how to manage your cycle.
Be advised, that although the side effects from anabolics can easily be managed in this day and age, you will need a host of ancilliary drugs to ensure safe use. Not for the faint-hearted. The sexual effects of 300mg+ a week of test, however, are outta this world!