Desensitization can be achieved through various chemicals. drugs, if you will.
For me, for example, an energy drink called Monster Java does the trick and lasts for a good 10 hours. This desensitization, however is for "sleeping so you dont get unwanted NEs".
If you are looking for desensitization so you can have sex without O'ing, there are a few options.
higher doses of Tramadol (if its legally prescribed of course) but the side effects (specifically how it affects your mood) dont make this a fun option
DXM, or Dextromethorphan, is a common cold medicine ingredient. It is the "high" that teenagers seek when "dosing" cold medicine. However, in moderate doses (too low to get "really high" and trip, but more than the label suggests) it can desensitize you IMMENSELY. HOWEVER, seperating DXM from the other nasty ingredients is not easy, when considering 99% of the cough syrups out there. However, there is ONE cough syrup that contains only DXM (Delsym) but it is in a slow-release form, therefore making it somewhat tricky to find the right dose without going overboard. Overboard wont hurt you, but Im not a fan of being "high" off DXM. The nice thing is tho the next day, you will STILL feel somewhat desensitized. Delsym can also be bought over the counter.