The guideline was released on Monday and officials will move to finalise it after a 45-day public comment period.
US health officials are proposing the use of a common antibiotic as a way of preventing sexually transmitted diseases for gay and bisexual men.
It comes as the incidence of these diseases increases in the United States.
"Novel approaches are needed to address the STI epidemic, especially for populations disproportionately affected," the Centers for Disease Control and Prevention (CDC) proposal states.
The new proposed guideline is based on multiple studies showing that some people who took the antibiotic doxycycline within three days of unprotected sex were far less likely to get chlamydia, gonorrhoea, and syphilis infections.
This "represents a new approach to addressing STI prevention in populations at increased risk for these infections," the CDC said.
The proposal was released on Monday, and officials will move to finalise it after a 45-day public comment period.
The guideline is specific to the group that has been most studied - gay and bisexual men and transgender women who had an STD in the previous 12 months and were at high risk of getting infected again.
There is less evidence that the approach works for other people, including heterosexual men and women.
But that could change as more research is done, said Dr Jonathan Mermin, who oversees the CDC's STD efforts.
'Didn't feel like we could wait'
Doxycycline is a cheap antibiotic that has been available for more than 40 years.
One study published in the New England Journal of Medicine earlier this year found that the incidence of gonorrhoea, chlamydia, and syphilis was lower by two-thirds when the antibiotic was given within 72 hours of condomless sex.
It has already been used by some local US health departments as a prevention measure.
A year ago, San Francisco's health department began promoting doxycycline as a morning-after prevention measure.
With infection rates rising, "we didn’t feel like we could wait," said Dr Stephanie Cohen, who oversees the department’s STD prevention work.
The drug's side effects include stomach problems and rashes after sun exposure. Some research has found it ineffective in heterosexual women.
Widespread use of doxycycline as a preventive measure could, theoretically, contribute to mutations that make bacteria impervious to the drug.
That kind of antibiotic resistance hasn't materialised in San Francisco, but it will be important to watch for, Cohen said.