Physical effects: Increased libido On the 3-MMC page this effect is cathegorised as a Physical effect. On the Mephedrone page it is classified as a Cognitive effect. It sounds like the 3-MMC's page describes this effect more precisely but this is open to discussion. Moreover, I have not used 4-MMC so I can't attest whether the quality of the libido stimulation is markedly different, cause it would make sense if the lust is more mind-present than bodily, if that makes sense. If there is no difference there, I will move this effect to the physical effects.
Yeah I can attest to 4-MMC being more lusty, 3-MMC affects libido as more physically horny than deeply arousing
After having a chance to try 4-MMC personally it seems like the serotonergic effects make it more lusty/randy + touch, kissing, hugging and everything romantic/sexual feels great, while 3-MMC seems like more straightforward physically sexual. My hypothesis is this is based in the weaker serotonergic and stronger noradrenergic release. When opening the discussion I was just under the impression the same effect should be in the same category in every substance but I see how many effect names may mean different things/spectra of the same phenomenon. Leaving this as is, unless someone has a different argument.
Oh, one more thing; 3-MMC lists orgasm supression and 4-MMC for me seems to have the same effect. Although it might have to do with the overwhelming vasoconstriction (I'm a male). I'd be interested in input from others, especially females (vasoconstriction might not be a problem to at least start intercourse for them) if they experience orgasm supression as well.