Repeated masturbation will cause acetylcholine/parasymphathetic nervous reaction which will over produce sex hormones and neurotransmitters like dopamine, serotonin and acetycholine. If these hormones are in abundance they can cause the brain and adrenal glands to produce large amount of dopamine-norepinephrine-epinephrine conversion, meaning their body system changes when repetitive masturbation occurs..
IMO, more than once in 10 or maybe 14days is excessive.
About sex.. Yes, its different because of oxytocine and vasopressin. Part of the effects of oxytocin and vasopressin may be due to their influence on dopamine in the reward circuits of the brain
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In my theory, excessive mastrubation(dopamine insensitivity) screws the reward circuits.
There are some theories about OT, VA and dopamine interaction..One of them is that OT and VA get in a way of the dopamine and norepinephrine which blocks the lust and allows the bond to grow. But still.. this is uncharted territory for neuroscientists. There has been some studies done on animals but for better understanding they have to do more research on humans. There are some studies, indicating oxytocin reduces stress in human beings. Thats one plus! as we know masturbation raises cortisol.