Aim: To evaluate the antireproductive effect of paracetamol in male rats. Methods: Male rats were orally administered daily with 500 mg/kg or 1000 mg/kg of paracetamol for 30 consecutive days. Their sexual behaviour and fertility were evaluated using receptive females. Results: At 2 h after treratment, sexual behaviour was not inhibited but on day 30 both doses of paracetamol caused marked impairment of libido (assessed by % mounting, % intromission and % ejaculation), sexual vigour (number of mounts and intromissions and copulatory efficiency) or sexual performance (intercopulatory interval). In mating experiments, the fertility (in terms of quantal pregnancy, fertility index, implantation index and number of implants) was significantly reduced. All these effects were reversible. The antireproductive effect was not due to a general toxicity but due to an increase in pre-implantation losses resulting from oligozoospermia, impairments of normal and hyper-activated sperm motility, and reduction in the fertilizing potential of spermatozoa. Conclusion: Long-term use of high doses of paracetamol may be detrimental to male reproductive competence.

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