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Injected plugs

Injected plugs were developed in China as a potential alternative to vasectomy. The concept is similar to the Intra Vas Device, except instead of implanting pre-formed plugs, the plugs are injected into the vasa deferentia in liquid form. The plugs then harden in place and block the flow of sperm. Two different types of injected plugs have been tested: medical-grade polyurethane (MPU) and medical-grade silicone rubber (MSR). Starting in the early 1980s, thousands of Chinese men chose MPU plugs as an alternative to vasectomy. Estimates of the number of men with plugs range from 13,500 to 300,000 (Zhao 1992b). World Health Organization (WHO) and Chinese government sponsored research on MPU plugs has been ongoing, but the results of studies initiated after the mid-1990s remain unpublished.

How does it work? How is it delivered?

MPU and MSR plugs are made by mixing two ingredients that are liquid at room temperature, which together form a polymer that sets within minutes. Without making any incisions, the polymer is injected directly into the vasa deferentia, the tubes carrying sperm from the testes. The polymer is kept in one area of the vas by clamping the tube on each side of the injection area. Once injected, the polymer solidifies in place, forming a flexible plug. In order to fully block the vas lumen (the opening in the vas tube), 0.16-0.22 milliliters of the polymer is injected until the vas visibly bulges (Zhao, 1990). The whole process takes less than 30 minutes, and is an outpatient procedure performed under local anesthesia. Once in place, the plugs can not be felt. Injected plugs are similar in function to a vasectomy, but its proponents believe it is easier to reverse .

How effective is it? How long does it take?

The two different types of injected plugs, MPU and MSR, have different track records in terms of effectiveness. Because it is being offered as an alternative to vasectomy, the researchers have set azoospermia (complete lack of sperm in the ejaculate) as their definition of effective. This may be an unnecessarily stringent standard, as the male hormonal contraceptive research community has agreed that 1 million or fewer sperm per milliliter is highly effective contraception. Unfortunately, few of the researchers working on injected plugs reports the sperm counts of their trial participants, choosing instead only to report what percent reach azoospermia. It is unknown how many of the non-azoospermic men in these trials have 1 million or fewer sperm per milliliter.

MPU plugs

MPU plugs have good results in large-scale clinical trials, with the largest group of 12,000 men showing 98% azoospermia (Zhao 1990). Unfortunately it takes months for MPU plugs to reach this level of effectiveness, with a slow but steady ramping up over 18 to 24 months. One small trial tracked 53 men given MPU plugs to see how long it took for them to reach azoospermia: 4% of the men were azoospermic after 1 month, 9% after 3 months, 38% after 6 months, 68% after 9 months, 85% after 12 months, and 96% after 18 months. At 24 months, there was no further improvement in effectiveness; the researchers blame this on misshapen plugs (Chen 1992). A larger trial of 1064 men showed 68% azoospermia after six months, and 98% after two years (Griffin 1996). Ninety-eight percent azoospermia was the same rate achieved by no-scalpel vasectomy in that trial, proving MPU to be a very reliable form of contraception.

MSR plugs

Studies of MSR have yielded varied results, and the research community has abandoned it. Initial studies in Asia were very promising. One trial of 14 men in China showed that they all became azoospermic 5-9 months after the procedure (Zhao 1992b). Another trial of 58 men in Indonesia showed 98% azoospermia after only 6 months (Soebadi 1995). This result became the subject of controversy when a WHO-sponsored study of Dutch men was cancelled due to poor results. In that study, “only 5–10% of the men became azoospermic, 80% became severely oligozoospermic… and the remaining 10-15% had reduced sperm counts” above 5 million/milliliter (d’Arcangues 1998). The Dutch researchers hypothesized that their low effectiveness rates might have been due to insufficient material injected, or insufficient pressure during the injection (Griffin 1997). Various researchers have hypothesized that MSR may be too soft to form an effective plug (Gu 2005), and the WHO has dropped it from their list of male contraceptive research priorities.

What side effects are expected?

Because there is no incision required by the MPU injection procedure, injected plugs have a very low complication rate. It is certainly lower than the complication rates reported for a standard vasectomy. At 0.85%, it is also slightly lower than no-scalpel vasectomy’s 1.21% and chemical vasectomy’s 1.31% complication rates. The reported complications included pain at the site of the injection (0.19%) and swelling of the epididymis (0.66%) (Griffin 1996).

It was concern about potential toxicity of a chemical component of the MPU polymer, aromatic amines, that led to the study of WHO-approved MSR. However, MPU plugs have been in used by thousands of Chinese men since 1983 with no reports of toxicity (Zhao 1992b).

Finally, there is a competing theory of why MPU plugs require so much time to become effective. Another group of researchers has proposed that MPU plugs rupture the vasa deferentia, and it is the slow formation of scar tissue that eventually blocks the flow of sperm. In this study, 10 men who had received plugs 4 years earlier requested reversal. The researchers found that all 10 men had ruptured vasa deferentia, with the leaked MPU embedded in scar tissue (Chen 1996). However, in a study of 49 Dutch men, there was evidence of vas rupture in only one man (Griffin 1997). If the formation of scar tissue is the main contraceptive mechanism of MPU plugs, the reversal success rates should be just as low as vasectomy reversal. MPU reversal studies show that this is not the case.

How long does it take to reverse?

As with the onset of effectiveness, reversal of MPU’s contraceptive effect is slow but steady. The reversal procedure requires outpatient surgical removal of the plugs under local anesthesia. One reversal study of 130 men, some of whom had the plugs in place for 5 years, reported 85% of the men were back to pre-treatment sperm counts within 2 years. The remaining 15% of the men had to wait up to 4 years for the full return of fertility. All these men were able to conceive after the reversal procedure (Zhao 1992a). Another WHO-sponsored trial completed a 3 year follow-up of 75 men who had their MPU plugs removed. In that time, all but one of the men conceived, whereas only 66% of the men who had a vasectomy reversal (vasovasostomy) were able to conceive in that time. As soon as 3 months after the reversal, the men in the MPU group had higher sperm concentrations than vasovasostomy group. The men in the MPU group also had lower sperm antibody counts in their bloodstream than vasovasostomy group (d’Arcangues 1998).



  • Chen, ZW, YQ Gu, XW Liang, ZG Wu, EJ Yin and LH [sic] (1992) “Safety and efficacy of percutaneous injection of polyurethane elastomer (MPU) plugs for vas occlusion in man.” International Journal of Andrology 15: 468-72.
  • Chen, ZW, YQ Gu, XW Liang, LJ Shen and WZ Zou (1996) “Morphological observations of vas deferens occlusion by the percutaneous injection of medical polyurethane.” Contraception 53: 275-9.
  • d’Arcangues, C, PD Griffin, H von Hertzen, M Mbizvo and PJ Rowe (1998) “Technology development and assessment.” In Special Programme of Research, Development & Research Training in Human Reproduction Annual technical report 1997. World Health Organization, Geneva .
  • Griffin, PD (1996) “Methods for the regulation of male fertility.” In Special Programme of Research, Development & Research Training in Human Reproduction Annual technical report 1995. World Health Organization, Geneva .
  • Griffin, PD, C d'Arcangues, PJ Rowe and H von Hertzen (1997) “Technology development and assessment.” In Special Programme of Research, Development & Research Training in Human Reproduction Annual technical report 1996. World Health Organization, Geneva .
  • Gu, YQ (2005) Email correspondence with Elaine Lissner, Male Contraception Information Project. 2 November.
  • Soebadi, DM, W Gardjito and HJA Mensink (1995) “Intravasal injection of formed-in-place medical grade silicone rubber for vas occlusion.” International Journal of Andrology 18, Supplement 1: 45 -52.
  • Zhao, SC (1990) “Vas deferens occlusion by percutaneous injection of polyurethane elastomer plugs: clinical experience and reversibility.” Contraception 42(5): 453-9.
  • Zhao, SC, YH Lian , RC Yu and SP Zhang (1992a) “Recovery of fertility after removal of polyurethane plugs from the human vas deferens occluded for up to 5 years.” International Journal of Andrology 15: 465-7.
  • Zhao, SC, SP Zhang and RC Yu (1992b) “Intravasal injection of formed-in-place silicone rubber as a method of vas occlusion.” International Journal of Andrology 15: 460-4.