| Hormonal Suppression of Sperm Production |
| Gonadotropin hormone- releasing hormone (GnRH) coupled with protein |
- Stimulates immune system to inactivate the body's natural GnRH, suppressing sperm production
- Annual injection
|
Two-year safety trial of gonadotropin hormone-releasing hormone (GnRH) combined with tetanus toxoid protein recently begun in 20 men. |
| 7-alpha methyl-19-nortestosterone (MENT) |
- Suppresses sperm production
- Annual implant
|
Efficacy trials of MENT implant under way; long-term toxicology testing not yet conducted. |
| Testosterone buciclate (TB) |
- Suppresses GnRH secretion and thus sperm production
- Three-month injection
|
TB injectable tested in a WHO-supported study indicates stronger dosage necessary for reliable contraception. Trials of TB injectable and progestogen may begin in 1998. |
| Testosterone undecanoate (TU) |
- Suppresses GnRH secretion and thus sperm production
- One or two-month injection
|
Studies among men under way in China of TU injectable; studies of two-month TU injection with a progestogen planned. |
| Testosterone enanthate (TE) |
- Suppresses GnRH secretion and thus sperm production
- Weekly injection
|
Provided effective contraception in 98 percent of 399 men in a two-year WHO trial, but not considered desirable for general use because weekly injections are required. |
| TE/progestogen combination |
- Suppresses GnRH secretion and thus sperm production
- Weekly injection of TE, daily progestogen pill
|
Combination of TE and progestogen achieved initial contraception sooner than TE alone, but not considered desirable for general use because weekly injections are required. |
| Non-hormonal Suppression of Sperm Production |
| Gossypol |
- Suppresses sperm production
- Daily pill
- Irreversible in some men
|
Recent pilot study of low-dose gossypol pill indicates effective contraception without dangerous potassium depletion. Larger efficacy study of 320 men planned. |
| Inhibition of Fertilizing Ability of Sperm |
| Nifedipine |
- May prevent sperm enzyme action needed for fertilization
- Daily pill
|
Research planned to find variations of this drug that may specifically target sperm without producing systemic side effects. |
| Mifepristone (RU 486) |
- Makes sperm temporarily immotile
- Daily pill
|
Research is seeking chemically-similar compounds that may target sperm without producing mifepristone's undesirable side effects. |
| Sperm surface protein |
- Antibodies attached to sperm block fertilization
- Vaccine
|
Immunization of male guinea pigs with sperm surface protein has demonstrated reversible contraception. Other animal studies planned. |
