Reproductive toxicity refers to the potential risk from a given chemical, physical or biologic agent to adversely affect both male and female fertility as well as offspring development. Reproductive toxicants may adversely affect sexual function, ovarian failure, fertility as well as causing developmental toxicity in the offspring. Lowered effective fertility related to reproductive toxicity relates to both male and female effects alike and is reflected in decreased sperm counts, semen quality and ovarian failure.

Infertility is medically defined as a failure of a couple to conceive over the course of one year of unprotected intercourse. Primary infertility indicates that a person has never been able to achieve pregnancy while secondary infertility is defined as a person having at least one pregnancy before. As many as 20% of couples experience infertility. Infertility may be caused by an issue along any part of the process of fertilizing an egg through birth of the child. This can include: the release of the egg, the ability of the sperm to fertilize the egg, the implantation of the egg in the uterine wall, and the ability of the fetus to complete development without miscarriage. Among males oligospermia is defined as a paucity of viable spermatozoa in the semen, whereas azoospermia refers to the complete absence of viable spermatozoa in the semen. Males may also experience issues in sperm motility and morphology, which means the sperm are less likely to make it to the egg or to be able to fertilize the egg. Female infertility could be a result of an issue regarding their uterus, ovaries, or fallopian tubes and can be impacted by various diseases, endocrine/hormone disruption, or reproductive toxicant.

The Globally Harmonized System of Classification and Labelling of Chemicals (GHS) separates reproductive toxicity from germ cell mutagenicity and carcinogenicity, even though both these hazards may also affect fertility.

Many drugs can affect the human reproductive system. Their effects can be

However, most studies of reproductive toxicity have focused on occupational or environmental exposure to chemicals and their effects on reproduction. Both consumption of alcohol and tobacco smoking are known to be "toxic for reproduction" in the sense used here.

One well-known group of substances which are toxic for reproduction are teratogens – substances which cause birth defects. (S)-thalidomide is possibly the most notorious of these.

Another group of substances which have received much attention (and prompted some controversy) as possibly toxic for reproduction are the so-called endocrine disruptors. Endocrine disruptors change how hormones are produced and how they interact with their receptors. Endocrine disruptors are classified as estrogenic, anti-estrogenic, androgenic or anti-androgenic. Each category includes pharmaceutical compounds and environmental compounds. Estrogenic or androgenic compounds will cause the same hormonal responses as the sex steroids (estrogen and testosterone). However anti-estrogenic and anti-andogenic compounds bind to a receptor and block the hormones from binding to their receptors, thus preventing their function. A few examples of the many types of endocrine disruptors are trenbolone (androgenic), flutamide (anti-androgenic), diethylstilbestrol (estrogenic), bisphenol A (estrogenic) and tributyltin (anti-estrogenic).

However, many substances which are toxic for reproduction do not fall into any of these groups: lead compounds, for example, are considered to be toxic for reproduction given their adverse effects on the normal intellectual and psychomotor development of human babies and children.