Sex Question Friday: Can Medications Be Transferred To Sex Partners Through Semen?

A reader submitted the following question:

“Can medications that men take regularly (like blood pressure, cholesterol, or diabetes meds) be passed through their seminal fluid to their oral sex partner? Many sex workers prefer to perform oral sex without a condom (bareback) and they often make the decision to swallow rather than spit. If medication can be passed like this, are these girls at any risk?”

Thanks for this very interesting question! Let’s first start by looking at whether medications that men are taking even show up in their semen at all. Research has found that this does indeed happen and that “seminal fluid chemical concentrations are typically similar to or lower than blood concentrations” [1]. So, medications and other drugs that men consume do appear in their semen to some degree, just as they tend to appear in other bodily fluids. However, keep in mind that the amount of ejaculate typically produced is quite small and, on average, consists of about one or two teaspoons. Thus, even though medications might be present in semen, this fluid is released in such small quantities that any potential chemical transfer through it would be very, very small.

The next question is how much of these chemicals are actually absorbed by men’s sex partners. Unfortunately, I can only address potential for vaginal absorption because that is the only sexual activity that has been studied in this context to date—thus, we cannot directly speak to how much absorption would occur through oral or anal sex, or with same-sex partners. We do know that absorption of medications through the vagina is at least possible (indeed, this is why doctors sometimes prescribe medications to be administered through vaginal suppositories–this absorbency of the vaginal walls is also why a small number of women have tried getting drunk through vodka-soaked tampons). However, because semen does not remain in constant contact with the vaginal walls and there is some degree of “leakage” after intercourse, it is unlikely that any medications present in semen would be completely absorbed through vaginal sex.

When you factor in both limited exposure and imperfect absorption, scientists conclude that chemical transfer through vaginal intercourse is unlikely to be “quantitatively important” [1]. Even if you assume complete absorption, a large amount of semen, and a very highly concentrated drug present in that semen, researchers still believe that the resulting transfer is unlikely to be clinically relevant.

As some additional evidence of this, a pair of studies was published last year looking at whether drugs known to have toxic side effects on a developing fetus can be transferred through semen. One study focused on humans and found no difference in likelihood of adverse pregnancy outcomes for men who were taking these drugs around the time that their female partners conceived compared to those who were not [2]. The other was an experimental animal study looking at transfer of chemicals to the developing fetus, which concluded that there was no “biologically meaningful exposure risk” of the medication through semen [3].

Again, I am not aware of any research looking specifically at medication-based semen transfer through oral sex; however, I would predict that the conclusions are unlikely to be much different, considering that the potential amount of a drug that could be absorbed through a single act is very small no matter what type of sex you’re talking about. That said, for a sex worker who performs multiple unprotected sex acts in a short period of time, the answer could potentially be different, especially if there is a lot of commonality in the medications/drugs used by the clients. However, in such cases, the risks of medication transfer are unlikely to be as consequential for sex workers’ health as their risk for contracting sexually transmitted infections.

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[1] Klemmt, L., & Scialli, A. R. (2005). The transport of chemicals in semen. Birth Defects Research Part B: Developmental and Reproductive Toxicology, 74(2), 119-131.

[2] Weber-Schoendorfer, C., Hoeltzenbein, M., Wacker, E., Meister, R., & Schaefer, C. (2013). No evidence for an increased risk of adverse pregnancy outcome after paternal low-dose methotrexate: an observational cohort study. Rheumatology, ket390.

[3] Breslin, W. J., Hilbish, K. G., Page, T. J., & Coutant, D. E. (2014). Assessment of fetal exposure risk following seminal excretion of a therapeutic IgG4 (T-IgG4) monoclonal antibody using a rabbit model. Reproductive Toxicology, 48, 124-131.

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