Sorry, but this thread is full of BS opinions.
My wife is an underwriter for United Health (and PacifiCare... Currently merging together) and before I started my first cycle we discussed this.
For starters, the doctor would have to write your situation up as caused by your "stuff" whether it is self induced or rubbed on like barry bonds.
Second, you pay for your coverage. As long as you do the annual check ups with your physician and get a clean bill of health, they cannot decline you coverage for anything unless you tried committing suicide. Any injury, reaction, or the like is what your insurance covers and is what you pay for. If you are declined coverage, the health insurance company is vulnerable to a major lawsuit if their refusal of coverage can't be justified. Steroid use is not listed as a precursor to deny coverage.
third... Slap the shit out of your doctor for even causing you an ounce of worry of this topic. It is not in his place to say who has what coverage. If he falsely states causes and effects of your symptoms and/or reasons you would need to see a doctor do to steroids, he can have his licensed suspended or revolked unless he is a current sports medicine specialist with a certificate in drug abuse/addition specialist to even be able to pinpoint your steroid use as a cause. It also sets him up for a lawsuit by you. Worst case scenario, you would see a doctor for either bad gear (alergic reaction/poisoning) or injection into the bloodstream. Injection into a blood stream is listed as either drug overdose or unprofessional misuse of a controlled substance. A reaction is handled as the same as a reaction to a bee sting. Either of those cases would not give right to the doctor to transcribe the cause as steroid use unless they did a test and got the results back before you left the medical facility. Highly unlikely. Test usually take 3-5 days if not longer.
A heroine addict gets full coverage medical insurance without amendments or listed and noted disclosures of a substance addiction. This can only be placed in the policy officially if the addict went through treatment previously or was arrested for it.
You are fully covered without issue while cycling. You know the personal risks so be careful.