As the name indicates it is an injection that is administered to the arm or buttock every 12 weeks. It is an effective method for people avoiding the pills and also for women who are sensitive to estrogen containing hormonal methods. Women opting for this method should not be afraid of shots.

 
There are two types of injections. They are Depo-Provera which lasts for 12 weeks and Noristerat which lasts for eight weeks. Depo-Provera is the most common injection. It contains progesterone which thickens mucus in the cervix therefore prevents sperms from reaching an egg. It also prevents an egg from being released through ovulation and makes the lining of the womb thinner so that it is unable to support a fertilized egg.  If used correctly its more than 99% effective.
This method of contraception can be obtained from dispensaries, HTC centers, private clinics, health centers, nursing, maternity homes and hospitals.
 
Advantages
•They are highly effective and safe
•It lasts long (8-13 weeks)
•Does not interrupt sex
•It’s an option for those that cannot use oestrogen containing methods such as the patch or combined pill
•It is safe for breastfeeding women
•May reduce heavy painful periods and help with premenstrual symptoms for some women
•May offer some protection from pelvic inflammatory disease and cancer of the womb. 
 
Disadvantages
•Periods may change causing one to experience irregular, heavy, short or light or no periods at all. This may settle down after a year or more of usage.
•It may take a while for natural fertility to return after one stops using the injection. It’s estimated that it might take 12 weeks for injected progestogen to leave the body. It may take longer for one’s normal period cycle to return.
•One may gain weight particularly if you are below 18 and overweight with a BMI of 30 and above
•Other side effects reported by women include; loss of sex drive, headache, changes in mood, tender breasts and acne.
 
References
The contraceptive injection. NHS choices. GOV. UK. Removed from: http://www.nhs.uk/conditions/contraception-guide/pages/contraceptive-injection.aspx#How
Injectables. C 2015 Marie Stopes Kenya. Removed from: http://www.mariestopes.or.ke/contraceptives
Hormonal Methods. C 2014 Boulder Valley Women’s Health Center. Removed from: http://www.boulderwomenshealth.org/our-services/birth-control/hormonal-methods/