5 days ago I received unprotected fellatio from a sex worker at an Asian massage parlor. I woke up experiencing immediate regret and panicked about the possibility of STDs.

I also read online about the use of doxycycline as a preventative and had some of that available from a past prescription. Over these 5 days I have taken 200mg of doxy per day. 

I know that the percentage chances are low, and I have no obvious symptoms of an STI. I know that gonnorhea is the most likely STI to be transmitted via oral sex, and I have had no discharge or abnormal pain during urination. 

My question is essentially whether I can breathe finally and rest assured that I do not have an STI. 

This is not an experience I will ever repeat again, so I just want to feel safe and assured that I am in the clear. 

As you understand (intellectually if not emotionally) this indeed was a near zero risk event. I would have advised against the doxycycline -- and you have been way overrated. The research behind doxycycline post-exposure prophylaxis (doxy-PEP) shows a single 200 mg dose to be effective in preventing syphilis and chlamydia. But you at virtually zero risk for either of these, so on that basis there was no point; and doxy-PEP reduces but does not eliminate the possibility of gonorrhea, because half of all gonorrhea strains are resistant to it. That said, absence of symptoms (urethral discharge, painful urination) is itself nearly 100% reliable evidence you didn't acquire gonorrhea.

So at this point I recommend you stop taking doxycycline and do your best to stop worrying. There is no point in being tested for anything.

I hope these comments are helpful. Let me know if anything isn't clear.

HHH, MD

Truth be told, the doxycycline was originally prescribed to treat acne and I never took it because it made me nauseous. My train of thought on that was the doxy would eliminate nearly any potential for an STI and also treat an existing condition.

Since I never plan on repeating the mistake, I truly just wanted to do everything possible to zap this error in judgment from my memory and body. 

I had deep dived enough of this forum to know what your answer would likely be, but wanted to thank you for providing an answer in my specific case. I’m hopeful this will help me reset my anxiety and move on. 

FYI, the normal dose of doxycycline for acne is 50 mg twice daily (or sometimes 100 mg for large persons) -- which would be less likely to cause GI upset. In any case, your first 200 mg dose provided maximum STI protection and you should not take any more for that purpose.