Questions and answers on injectables

How do they work?

Injectables contain a progestin like the natural hormone progesterone in a woman’s body. There are two types: medroxyprogesterone acetate (DMPA) and norethisterone enanthate (NET-EN).

Because these injectables do not contain estrogen, they can be used throughout breastfeeding and by women who cannot use methods with estrogen.

DMPA, the most widely used progestin-only injectable, is also known as “the shot,” “the jab,” the injection, Depo, Depo-Provera, Megestron, and Petogen.

NET-EN is also known as norethindrone enanthate, Noristerat, and Syngestal. 

Given by injection into the muscle (intramuscular injection). The hormone is then released slowly into the bloodstream. A different formulation of DMPA can be injected just under the skin (subcutaneous injection). See New formulation of DMPA, further down on this page.

Work primarily by preventing the release of eggs from the ovaries (ovulation).

In contrast, monthly injectables contain both estrogen and progestin. 

How effective they are?

Effectiveness depends on getting injections regularly: risk of pregnancy is greatest when a woman misses an injection.

If used correctly, the contraceptive injection is more than 99% effective. 

When women have injections on time, less than 1 pregnancy per 100 women using progestin-onlyinjectables over the first year (3 per 1,000 women).

Return of fertility after injections are stopped: An average of about 4 months longer for DMPA and 1 month longer for NET-EN than with most other methods.

Protection against sexually transmitted infections (STIs): none


What are the side effects?

Some users report the followings

  • Changes in bleeding patterns including, with DMPA:
    • First 3 months: Irregular or prolonged bleeding
    • At one year: Infrequent or irregular bleeding, or no period at all
      NET-EN affects bleeding patterns less than DMPA. NET-EN users have fewer days of bleeding in the first 6 months and are less likely to have no monthly bleeding after one year than DMPA users.
  • Weight gain

  • Headaches

  • Dizziness

  • Abdominal bloating and discomfort

  • Mood changes

  • Less sex drive

  • Other possible physical changes:

  • Loss of bone density

Why Some Women Say They Like Progestin-Only Injectables?

  • Do not require daily action

  • Do not interfere with sex

  • Are private: no one else can tell that a woman is using contraception

  • Cause no monthly bleeding (for many women)

  • May help women to gain weight


Known Health Benefits


  • Helps protect against:

  • Risks of pregnancy

  • Cancer of the lining of the uterus(endometrial cancer)

  • Uterine fibroids

May help protect against:

  • Symptomatic pelvic inflammatory disease

  • Iron-deficiency anemia


  • Sickle cell crises among women with sickle cell anemia

  • Symptoms of endometriosis (pelvic pain, irregular bleeding)

Known Health Risks: none


Helps protect against:

  • Iron-deficiency anemia

Known Health Risks: none

NET-EN may offer many of the same health benefits as DMPA, but this list of benefits includes only those for which there is available research evidence.


Correcting Misunderstandings 

Progestin-only injectables:

  • Can stop monthly bleeding, but this is not harmful. It is similar to not having monthly bleeding during pregnancy. Blood is not building up inside the woman.

  • Do not disrupt an existing pregnancy.

  • Do not make women infertile.

New Formulation of DMPA

A formulation of DMPA has been developed specifically for injection into the tissue just under the skin (subcutaneously).

This new formulation must be delivered by subcutaneous injection.

It will not be completely effective if injected in other ways. (Likewise, DMPA for injection into the muscle must not be injected subcutaneously.)

The hormonal dose of the new subcutaneous formulation (DMPA-SC) is 30% less than for DMPA formulated for injection into the muscle—104 mg instead of 150 mg. Thus, it may cause fewer side effects, such as weight gain.

Contraceptive effectiveness is similar. Like users of intramuscular DMPA, users of DMPA-SC have an injection every 3 months.

DMPA-SC will be available in prefilled syringes, including the single-use Uniject system. These prefilled syringes will have special short needles meant for subcutaneous injection.

With these syringes, women could inject DMPA themselves.

DMPA-SC was approved by the United States Food and Drug Administration in December 2004 under the name “depo-subQ provera 104.” It has since also been approved in the United Kingdom.